I didn't pay $200 simply for questions. The Kaplan Quiz Bank is the best way to do practice problems in my opinion because it allows one to do problems on a computer and build custom timed custom quizzes by topic and difficulty.
The product is an online quiz builder and allows the user to customize quizzes based on question type, content and level of difficulty. The quizzes can be taken in timed or tutor mode (untimed w/explanations provided during the problem). The questions are well written, which people don't seem to give Kaplan much credit for on its other products. However, this generalization doesn't apply to the Kaplan Quiz Bank and the Kaplan GMAT 800 book (with the exception of the CR and RC in this book). The quant questions are challenging and the easy and medium difficulty questions are similar to those one would see in the Official Guide. The harder quant questions are similar to the problems in Kaplan's GMAT 800. The verbal questions also mimic the writing style of those found in the OGv11. The CR and SC are excellent...if you saw the problems you would agree that they are of very high quality and are very similar to what one would see on the actual GMAT.
All questions have detailed explanations and can be flagged for review. Yes, it's pricey, but it costs the price of one test. I would rather pay the $200 for a large database of high quality, online problems and do well on the test, then try to save money by doing problems off of a piece of paper or heavy book, and not achieve my target score. Doing timed problems on a computer accomplishes three things: 1) it allows one to get used to completing and reading problems from a computer monitor (it's important to understand that doing problems on a computer and doing them using a heavy book are two different skills) 2) it helps build test taking stamina and 3) it allows one to to practice a variety of problems under timed conditions.
Furthermore, I think the OGv11 PS problems are not challenging enough to use for practice because they are not representative of the level of difficulty one will see on the real test. Moreover, one can't get good practice training his/her brain to "shift gears" in quant and verbal by doing 30 straight problem solving one day and then 30 DS the next and then 30 CR the following. It's best to practice quant by doing a mixture of PS and DS problems in one sitting. Why? Because PS and DS require different ways of thinking. When I do 30 straight DS problems I am in "DS mode" and my DS hit rate is usually better then my DS hit rate when I do a mixture of 30 DS and PS problems. This is because the mixed quiz requires me to "shift gears" back and forth under timed conditions, so this alone adds another element of difficulty to the problems.
The Kaplan Quiz Bank allows one to specify the quant topics one wants to be tested on. So for instance, if I want to work on number properties and algebra problems only then I can create a quiz of 30 problems that tests only these topics. I can tell the quiz builder to build a quiz of only medium and hard problems in PS and DS format. The quiz builder may start off with a hard PS number properties problem, then give me 1 DS algebra problem, then 2 PS algebra problems, then 2 DS number properties problems, etc. just like the real test. Practicing like this is more effective and can help one tackle their weaknesses more efficiently. And once the quiz is done one can see an analysis of his/her total hit rate and then his/her hit rate by problem type as well as by the level of difficulty. This was extremely helpful for me because I noticed that for certain topics such as proportions and algebra, my hit rate on the medium and hard problems was almost equal. The OGv11 doesn't allow one to do this and looking at hit rate without separating the hit rates by a problem's level of difficulty can be misleading. It's very important for one to get a higher hit rate on medium difficulty problems in order to achieve a 650+ score. The Kaplan quizzes told me which topics I needed to focus on in order to boost my hit rate on the medium difficulty problems so I focused on these. And sure enough my hit rates on the medium difficulty improved.
Same thing with CR, PS, SC and RC. I noticed that my SC hit rate was ~80% after doing a number of problems, but I then noticed that my hit rate on medium SC problems was actually lower than my hit rate on the hard SC problems. This was a major problem which I was able to fix with a lot of practice. However, I wasn't aware of this when I was using the OGv11 for practice because my overall SC hit rate was about 85%, but there was no way to tell how I was doing on the 600-700 level problems vs. the 700-800 level problems so I mistakenly thought I was doing "okay." I don't buy into the theory that the problems towards the end of the OG are harder and the ones near the beginning are easier.
I hope this helps explain why I spent $200 on this product. I highly recommend that others try this. Doing problems in this fashion gave me the intense practice I needed.