People often ask us to compare Synthesis with Roger van Zandvoort's Complete Repertory or with other repertories such as Kent, Knerr, Scholten, Murphy or Bonninghausen. (Note: Images are taken from MacRepertory on a Macintosh for convenience, MacRepertory for Windows would look very much the same.)
Let's start with Synthesis vs the Complete. Both of them are based upon Kent and hence both are Kentian style repertories. So if you know how to use Kent then you can use either Synthesis or the Complete with equal facility. Some things will be a little different but you will figure out where your favourite rubrics are very quickly.
There are arguments about who has the best and most original source material from Kent and from his annotated copies. In the end what matters is how accurate the repertory is. Speaking of the Complete, I have on a number of occasions pointed out errors or what I thought were errors to Roger vans Zanvoort, it's author. Mostly I've been wrong and I can state plainly that Roger is a stickler for getting it right. You won't win many arguments with Roger about the remedies in a rubric or such like.
Moving along, I would like now to refer to the Complete repertory 2009 (CR09). One of it's features, which distinguishes it from other Kentian repertories is the inclusion of Boenninghausen style partial rubrics. This is something of a boon as it allows the user to use these rubrics like they would those of the Therapeautic Pocket Book. What this means is that you are free to combine partial rubrics in the way Boenninghausen intended and if you wish and Kentian rubrics too.
The first thirty two rubrics in the image below are partial rubrics and this is the usual arrangement in that the partial rubrics are at the beginning of the list of rubrics.

In Kent's repertory we see below that the first rubric is Abscess.
One thing to keep in mind in all of this is the answer to the following question.
What is the minimum number of rubrics require to make a successful prescription?
Answer = 1.
So the long and the short of it is don't be afraid. There is nothing very new about the Complete 2009 or the Complete Classics Repertory. They are just bigger, more comprehensive, refined accurate and easier. So if you understand how to take a case and then how to choose what symptoms / rubrics are characteristic generals or peculiars, you will feel right at home with the Complete or with any other Kentian Style Repertory and you'll be delighted to discover how easy it is to find what you need, no matter which repertory it's in. After all we made repertorising easy. Others have followed our lead.
The hard part is deciding what rubric to use, not finding it.
Differences
One of the major differences is that while Roger van Zandvoort's Complete has maintained rubrics from Kent's repertory, this is not always the case with Synthesis. An example of this is the rubric:
Generalities; FOOD and drinks; Warm; drinks, water; agg./amel/aversion/desires, from the Complete 2009 and other editions of the Complete repertory.

In Kent's Repertory we have : -

You can see by comparing Kent with CR09 that CR09 is in keeping literally with Kent. In Synthesis, this rubric has been changed to "Hot drinks". If you think about it for while, I think you will come to the conclusion that Kent was right and that "Hot drinks" as found as a sub-rubric in CRO9 is the better arrangement.
Here is an interesting comparison of different repertories.
Complete Repertory Classics 2009 by Roger van Zandvoort
This is the subset of the larger Complete Repertory 2009 from Roger van Zandvoort and is a replacement for old, yet popular Complete Repertory 4.5.
CR Classics is based on a subset of CR 2009, filtered out are those rubrics that did not occur in Kent's repertories, Boenninghausen's repertories and the Synthetic Repertories (hence the name). In all rubrics from these forementioned repertories available in Classics, all remedies maintained are also available in Complete Repertory 2009. Cross-references are maintained for those rubrics available in Classics.
Repertory Kent ++ CR 4.5 CR 2005 Classics CR 2009 Synthesis 9.1 Number of rubrics with remedies 64 230 125 583 158 475 75 285 178 094 139 714 Number of remedies 624 1 536 1 846 2 126 2 393 2 373 Number of remedies that occur in at least 100 rubrics 362 587 942 990 1065 unknown Number of remedies that occur in at least 1000 rubrics 157 229 361 319 417 unknown Number of remedy occurences 503 145 932 636 1 546 403 1 247 288 1 913 599 1 066 987 Grade 1 338 879 720 027 1 078 098 829 212 1 327 303 816 612 Grade 2 129 362 171 064 ** 23 159 ** 42 063 ** 56 232 201 295 Grade 3 34 904 41 107 303 956 248 342 360 190 48 610 Grade 4 0 438 141 190 127 554 169 874 470 Number of additions clinically verified (grade 2 + 3 + 4) 164 266 212 609 285 739 417 959 586 296 250 375 Clinically verified, % of total 32,65% 22,80% 30,28% 33,51% 30,64% 23,47% Number of references and cross-references 0 52 066 131 993 67 033 216 530 28 744 Average number of remedies per rubric 7,83 7,43 9,75 16,56 10,74 7,64 Compensated repertory model Yes Yes Yes Yes Yes No
** In CR Classics 2009, grade four is grade three in the other repertories, grade three in CR Classics 2009 is grade two in the other repertories. Grade two in CR Classics 2009 is non-existent in the other repertories (Boenninghausen’s grade two means mentioned by two or more provers but no clinical confirmation)Synthesis Treasure
Kent CR 4.5 Synthesis Treasure Ed * CR Millenium CR 2001
/ RU ICR 2005
/ RU VCR 2008 CR 2009 Rubrics with remedies 64,230 125,583 139,553 146,622 151,316 158,437 167,474 178,094 Remedies 624 n/a 2,375 n/a 1,656 1,810 1,911 2,394 Average remedies per rubric ** 7.83 7.43 7.66 6.90 8.55 9.70 10.44 10.75 References & cross-references 0 52,066 28,764 87,981 114,127 132,017 186,972 216,577 Author (source) references n/a n/a 1,787,994 n/a 1,119,273 2,217,840 3,048,485 3,439,769 Remedy occurences 503,145 932,636 1,069,724 1,183,374 1,294,251 1,536,953 1,748,337 1,913,936 Grade 1 338,879 720,027 819,148 935,403 1,008,504 1,072,622 1,201,224 1,327,392 Grade 2 129,362 171,064 201,443 194,923 223,834 22,972 51,180 56,237 Grade 3 34,904 41,107 48,659 52,653 61,219 302,070 339,545 360,203 Grade 4 0 438 474 395 685 139,180 156,200 169,875 Clinically verified additions *** 164,266 212,609 250,576 247,971 285,738 441,250 495,745 530,078 % Clinically verified 32.6 22.8 23.5 21.0 22.1 30.3 28.4 27.7 Relative to Kent 0 1.3 x 1.5 x 1.5 x 1.7 x 2.7 x 3.0 x 3.2 x Availability n/a n/a n/a