They can be good for breaking up counter attacks. (let the FT's come up behind your advancing troops (usu. just the engineers they came with, engineers are faster than FT's, so it's logical that the FT's will be behind your advance line), if the enemy counterattacks, fall back quickly and let the enemy rush unprepared into your FT's. Sometimes you can get crossfire with two or more. Breaks infantry attacks nicely.
On offense, they are very hard to use, but can be used in special circumstances. I've used Ft's to destroy a supressed MG nest in woods/pines. I get all my troops to area fire the MG till he ducks, then rush the FT forward (who has been waiting 5 yards beyond what the MG can see, but still within 30 or so yards) and zap him. Normally the MG will either bolt or surrender. Of course, if the MG nest has correct overwatch, they need to be supressed as well.
I've also had some success in using FT's to attack enemy just over a ridgeline/cliff/ditch. I'm in the ditch, enemy up top (shooting down, or can't see me but close to edge) i set my FT to area fire up to the edge of the ditch. Area fire being what it is, fire goes everywhere on to the other side. Usually you can get the enemy to abandon position at least.
Best use for FT's that I've seen is flaming tanks. Not always 100% effective, but the percentage is very high, and it's more effective than most other infantry AT assets. Even one good gout of flame is enough to shock or immobilize the worst tank (IS-2, KT, Churchill). Plus, it's fun. And rough on the crew when they abandon the tank. Yes, Wasps and SPW-251/16's are far more effective.
As far as survivability, chose tight terrain, choose darkness, choose a foolish enemy. If you can. If I get a Steppe Map Mid-Day QB, my FT's hide and stay that way. Usually there's nothing you can do.
Zimorodok.