How do they manage the wallet in a secure fashion?
Given that a decent portion of the BTC community seems to be scammers of one sort or another, how does one know that theyre safe? Are they externally validated somehow?
Can't speak for the other clients, but with Electrum (which is the one I've been using for the last few weeks), both the client and servers are fully open source, with a compact and easy to review codebase. The wallet uses very strong encryption and the private keys are always stored on your PC, not in the cloud. It also has a very active development team and a lively userbase.
I'm not an expert, but I would say it's at least as secure as the bitcoin.org client. I haven't heard of a single security incident involving Electrum.