While Steve is correct regarding the coupler version of the CPR system, if you are just using it as a altimeter holder then it's a bit simpler. When I first started flying 15 years ago, PML kits were one of the few brands that were readily available and had good instructions for newcomers to the hobby. I bought a Sudden Rush for my L1 flight which used the PML CPR system to hold the altimeter. I really liked that system and have standardized it across my fleet - from 54mm to 7.5" N powered beasts. One thing I do differently is use a screw switch that does not require external wires. There is just a hole drilled in the ebay to allow access to the screw. The same hole also acts as the baro vent.
I've done dual deploy two ways - in large diameter (6" or greater) I can put two of the CPR mounts side by side, in smaller diameters I just use a 38mm tube long enough to hold two altimeters.
While I had decent success with their piston system, if you build it as they instruct it can fail. And Quantum tube is ok for smaller diameters but I don't think it holds up well in larger diameters or longer tubes.
The biggest problem with buying a built kit is that you are relying in the skills of someone else. Somehow I ended up with a bunch of rockets someone else had built and kept in their garage in the Texas heat. While they looked fine on the outside, the epoxy in the inside and become extremely brittle and even had shrunk a bit. Some fins I could pull right out with just a bit of wiggling back and forth. The other issue is that G10 (and Quantum tube) need to be properly prepared for Epoxy to bond well and if not done the joints can be very weak.
I"ve bought and flown several rockets built by others and have generally had good luck. But it's always good to be able to inspect first and talk to the builder to make sure you know what you are getting.
Good luck,
Tony
