Tubular Heating

Has anyone used 60,80,120 watt tubular heaters? i have been told they was ok but now i have been told that they suck.
Just wondered if anyone had used one before if so what wattage was it and how warm did it keep ur grow tent?

Ive used them in a 12x6ft shed 4X80watts and they were sound

Ok well just for those who dont know alot abot them.. i got 1x120watt from argos and it makes temps rise by around 4-5 celcius.
Hope that helps anyone looking at buying them.
Also they are designed to be left on 24/7 no problems ( well thats what the instructions say)