For me, the value of the test sites was not the questions asked but, rather, the paragraphs that explained, in broad terms the topics in the question.
I used JBL and a couple of apps on my iPhone. Not one site had questions that replicated the style of the NREMT (which I took last month.)
I found Christopher Coughlin's "EMT Crash Course" to be very helpful; it simplified the material by sifting out the minute details that are beyond the scope of what's on the test.
The NREMT web site will tell you the proportion of questions from the potential topics. I found making outlines of things like pregnancy complications, delivery complications, vitals, respiratory issues, and cardio issues to be very helpful.
Good luck. The test will make you feel stupid. But, most likely you will pass.