I've been using beta branches of Destiny Item Manager for a while now and nothing's gone wrong. All these apps use Bungie'a API, so if anything went wrong with them, the save could happen with the Destiny app or website
I would buy this dev a beer. He updates Tower Ghost almost every single day. And he has apps for Android, Blackberry, Chrome, Firefox, Amazon Kindle,
Windows Phone (not even Bungie has that), and is working on bringing one to iOS that is in beta. And he updates them all almost daily.
Mad respect for all that hard work. The app is amazing. You can sort your weapons in a number of ways. My personal favourite is to filter out all my maxed out weapons so I can see at a glance what gear I still to level up with XP. And you can turn on tooltips for all the gear that is taken from destinydb.
The app will not only automatically transfer items to the character you want, but it will also move around any un-needed items back to the Vault if you don't have space, AND it will even equip items for you all at the same time so long as you're in orbit.
I've set up Loadouts to easily transfer all the weapons I might need to one of my 3 characters depending on what I'm doing.
I have one for:
Solar Burn: Vision of Confluence, Black Hammer, Gjallarhorn
Arc Burn: Fang of Ir Yut, Fatebringer, Plan C, Song of Ir Yut
Void Burn: Word of Crota, Sword Breaker, Truth
Vault of Glass: Fatebringer, Gheleon's Demise (fatebringer perks), Ice Breaker, Sword Breaker, Praetorian Foil, Gjallarhorn, Hunger of Crota
Crota's End: Word of Crota, Red Death, Vex Mythoclast, MIDA Multi Tool, Gheleon's Demise, Black Hammer, Ice Breaker, Sword Breaker, Gjallarhorn, Hunger of Crota
Crucible: Thorn, Felwinter's Lie, Corrective Measure
Iron Banner: Same as above, except that I have it equip my favourite armours on my Warlock, too.
I've made sets for Iron Banner and the various Burns to quickly transfer those items to characters, 'cause a player ain't got time to wait.
I don't know if your fear is justified, but I share it with you.
Yeah I was apprehensive at first, but it uses the same features as the official Bungie app, and you can't dismantle items outside of the game anyway. I've never had a problem. The only thing it won't do is transfer an item that you already have equipped (edit: when you're in-game - works if you're in orbit/tower). You must first equip something else, then it'll do it. Also, he makes all the code available
open source!