I've used them a fair amount, actually, just never in large units. I suppose if you take a full compliment then yes, the Ethereal is as safe as anywhere else while on foot. I generally think any Ethereal on foot is dead meat, though. Ten Sniper Drone wounds aren't all that great, though I suppose if you play the target priority game they can last.
As to sniper weapons' utility, you're right that they can kill things, but they aren't ideal against much beyond Monstrous Creatures. You'd get more mileage against most targets by devoting your points to different units that do the job better. Anti-infantry fire is well covered by Firewarriors, Hammerheads, various crisis suit builds, Riptides, Stealth Suits, and so on, and many of them also have utility against other targets, too.
I think Sniper Drones have a place, sure. I don't, however, think they're the strongest choice in the codex by far.