Hey Rafael, good to see you here on TRF. Sharon and supplied the motor you used for your L1 cert. at Eagle Eye last month. Glad to see you working up into dual deploy, it will help you recover rockets at our launch site, a daunting task to say the least.
I have most of the altimeters mentioned in this thread, and my favorites are the Stratologger SL100 and the RRC2+. I have about a dozen dual deploy rockets, and Sharon has several more that use Stratologgers as primary, and RRC2+ or RRC3's as backup. For your first altimeter, you can't beat the new Stratologger CF, but the RRC2+ is cheaper and just as easy to use. I like Stratologgers because I download data to my laptop to keep track of my flights. The RRC2+ doesn't have that function, but will do the job it was designed for. If you like DATA, The RRC3 will give you lots of it, more than the Stratologger. I started out with a Stratologger, and honestly don't know how many we have in our rockets. When they came out with the new CF design, we bought a few for new builds. I'm putting one in a new minimum diameter Blackhawk 54 with an RRC2+ as backup. The avbay is so small, it wouldn't fit the older Stratologger SL100 or the RRC3.
I have also built two Eggtimers and at least four Eggfinders. I can't recommend an Eggtimer for a first altimeter, it's too complicated to set up, and you have to build them, which adds another level of complication.
Whatever you decide on, I would be glad to help you with advise on how to set it up in your rocket. Or you could just look at one of my many build threads here, I have several that detail the way I build avbays.