I think they're generally used short term but I really can't see one breaking. They do come in varying qualities and I'd certainly go for a more sturdy one
I used a 90 litre plastic storage tub for rearing over 400 livebearer fry for around 7 months,seemed to work for me,i'm not sure long term whether they would be suitable though...
I did find near the end with mine the heater,although not close to the plastic,it did start melting the side of the tub,thats why i stopped using it.
You can find large sturdy plastic containers at garden centre's...but also you can pick up cheap second hand tanks if moneys a issue..i always go second hand
The biggest disadvantages that I see to plastic tubs long term is that it doesn't let you see your fish and attaching filters or heaters is more difficult. I think we have all used tubs for a short time, as Harlequins said.
Plastic tubs make great cheap fry tanks and emergency hospital/quarantine tanks too. If you get a good quality sturdy one you won't have any problems. I kept my coldwater fish indoors all winter in 2 huge plastic crates and the crates are still OK 5 months later
Right you are Fishnovice. I find that plastic tubs make great temporary storage for fish. The other side, which I tried to show with my post, is that a temporary housing solution is not nearly the same as a permanent home.