Wilson/WeBoost are the gold standard for consumer Amps. I would check their site. I have a cradle amp, the Wilson Sleek and love it. Makes a huge difference.
One thing to be aware of though for the retail amps that you do NOT cradle the phone, the range is very small. You will not cover the entire inside of your rig with one of them (even a tiny RV). In fact I saw a review confirming this, just the other day on YouTube on RV with Tito. He reviewed one of the newer WeBoost non cradle amps and he found that he had to be within a few feet of the amp to get a usable signal boost from it.
