They had the same deal on the iPhone 6s/6sPlus and I traded in a four year old Droid 3 for $100. The volume up button didn't work - still got the promised $100. I actually wasn't going to bother, because I figured they'd give me nothing for it, and ended up doing the web site after about a week, just to see what would happen and was surprised it was that much.
You can get an appraisal if you add the device to the cart and go through checkout, but before you actually checkout. In fact, I just did it (I'm going to cancel - I'm not planning to buy a Turbo 2), using my old Droid Maxx. I selected "with cracked screen" (even though mine is uncracked) and the appraisal is still $300.