Radio Poppers have two basic models, PX and JrX. The PX system is the full function (CLS/TTL compatible to 1500 ft). The JrX system is for manual triggering with remote power adjustment from your camera. I believe the systems can be mixed to control both TTL and manual lighting.
I have the PX system with either an SB-900 or SU-800 as the commander. It uses two types of attachment. First, the Radio Popper Receiver comes with a plastic stand with 1/4 inch female metal screw mount in the base. It mounts on a light stand or anything else that has a 1/4 male screw. The plastic stand also houses the Radio Popper receiver and the speedlight. They work nicely. I have 2 SB-800s that are always mounted in the brackets so all I have to do is screw them onto the light stand and I am ready to shoot. This is a definite improvement over the original velcro attachment.
Second, the Transceiver mounts to your commander unit (Speedlight or SU-800). Yes, it is still done with velcro, but it is very secure and I have no problem with it. Since my Pelican case and bags have velcro, I velcro them to the case/bag so they don't get "lost in the bag" when not in use.
One of the unadvertised features that I like is the battery meter. I can check at any time to see if I need new batteries or a charge before I go out to shoot. If I start with a reasonably full battery, I can shoot all day.
Before I bought my PX system, they changed the switches from dip switches to the little bubble switches. They work, but in bright sunlight, seeing if the light is on is a challenge for my eyes. It is very easy to see indoors.