I use the Featherweight magnetic switches on all of my rocket electronics, very happy with them, and haven't had any fail for me yet. I've used them to power Eggtimer/Eggfinder units, StratoLoggers (SL100 and SLCF) as well as EasyMini's, and will be using it for illumination power on my night launch rocket when I get that far with it. I've always used a 2s 950mAh LiPo (Turnigy Nano-Tech) with all my electronics. I still recommend a hole however, for 3 reasons:
1) Easier to know where to swipe the magnet.
2) Can line the hole up with the LED on the magnetic switch for visual confirmation that you successfully turned things on/off
3) Barometric altimeters need ventilation anyhow, so I make this hole one of the altimeter's static ports and let it do double-duty.
The only place I haven't succeeded with #3 is my Nike Smoke, where the electronics are in the nose and I can't get the magnetic switches close enough to the side-walls of the cone at its base where I put the vent holes (since my opening into the nose is a good bit smaller than the nose itself), so I needed two holes farther up for the Eggtimer TRS's two battery connections. These are still marked with holes, but I'm going to plug them with a clear epoxy to make them translucent but not ventilation points.
I have experienced the 'chatter' with these switches, where sometimes swiping you get a quick off->on->off, or on->off->on. With the StratoLogger things aren't so bad since it's pretty much always making noise when powered, so as long as you can hear it you can tell if you succeeded (it's harder with the SL100 because its cap keeps it running a few seconds after power is lost, so you need to keep listening for a while). Other altimeters aren't nearly as noisy so without seeing the LED it would be much harder to tell if it's on or off. They're also more sensitive to passing the magnet in one orientation relative to the PCB than the perpendicular orientation, so take note of how you have the switch oriented for any given rocket and you'll have better luck turning it on/off the first time. I can't always orient mine the same way for space/wiring reasons, so some rockets I have to pass the magnet along the rocket length-wise, other ones around the circumference, if I go the wrong way on a given rocket I find they're harder to activate/deactivate.