I took the exam and UW is simply a learning tool so using it in timed mode is a waste of time if you have no issues with finishing blocks on time.
I agree... if you're a quick test taker.
When I was studying for Step 1, I started off doing timed/random. Always finished with enough time to go back and check some questions. It was a useful enterprise for getting used to the pace of the exam, which is VERY important or you're in for a rude awakening on test day. I know people who were EXTREMELY pressed for time with Step 1, so I think its dangerous to call timed mode a waste of time until you've done it.
After a while, I switched over to untimed/tutor. I found it more useful to see if I was 'thinking through' questions the right way with the instant feedback about my answer. I think tutor mode is a much more effective way if your goal is to learn the material in the questions.
So, yeah, do both. If I could go back, I'd do more tutor mode early on (when you're still learning the material) and more timed blocks late (when you're more double-checking your fund of knowledge and getting into test taking mode). UWorld in 48 question blocks, timed and random, is so much like the actual test it will blow your mind. When I was taking the real thing, at times it felt like I was just doing another UWorld question block.
What do you think about working through UW twice, versus another question source and then UW towards the end? Do you think doing all the questions 2x diminishes what you get out of it?
No way. There's, what, 2000 questions in UW? You forget the questions long before its time to repeat the qbank.
I did all of UWorld once, then went back and did all of my incorrect questions once more. I felt like that was more than ample questions.