Thanks for your helps guys.
As for the difficulty of Kaplan's Quiz Bank, it ranges from Low to High. It lets you choose if you want Low, Medium, or High level difficulty. It also lets you pick which question types you want. So in:
RC, it lets you pick Business, Social Sciences, Sciences, etc.
SC: lets you pick which errors you want to test yourself on
CR: Different CR Types
Quant: PS or DS and then split by topics such as NP, Geo, Arith, Algebra. However, it doesn't split topics further down - so Geo cannot be split into Triangles, Polygons. This is one drawback.
But overall, I really liked Quiz Bank. I has 1400 questions which means you can create almost 19 "informal" CATs (1400/74). What I like the most is that the questions are on-screen and in same format and look like a CAT. So, you can write 37 Geometry focused questions followed by 37 CR questions and it builds you the stamina of writing a CAT.
But the question language is slightly off from OG questions, so I think I'll be focusing on OG for the next 2 weeks.