I carried an AAA Mag Solitaire on my keychain for years. I didn't use it much, but it was fairly reliable, albeit yellowish light and short runtime. I also had to replace it every year or so because the finish wore off. I've carried an ARC AAA on my keychain for over a year now, and it is far superior to the Solitaire. The only advantages the Solitaire has over the ARC AAA are the much lower cost ($5 vs $25), and the ability of the Mag to focus its beam and with a fresh battery, out throw the ARC if it is focused to a spot, although with much less overall light output. I've got four Solitaires that sit in a drawer now and aren't used. The Mag Solitaire isn't completely bad IMHO, but only with a fresh bulb, a fresh battery, and clean battery/switch contacts. The Mag isn't terribly useful after the first 20-30 minutes of battery use.
-Keith