As Jim said the can be expensive to run so efficiency is what is called for.
Like you I researched heaters through A4A and it was Laurie who put me on to this company;
I bought this one;
http://www.parwinheatersukltd.co.uk/I purchased the 3kw Pe 1 in January 2010 so this year was my first FULL winter and during that really cold spell it worked a treat.
I had it set to keep my greenhouse at around 2°C (37°F) all winter and it did.
I have a 'wireless' monitor in the house which monitors the heat in my greenhouse without having to venture out in the ice and snow and it did what I had set it to do!
OK it is not cheap but it is accurate and can be used as a cold fan in summer if required.
Plus you can set the fan to only come on when the heater kicks in.
What I like about it is the thermostat!
I find it very accurate so there is no wasted heat unlike some cheaper varieties which can have an accuracy of +/- 5° meaning these can remain on well after the temperature is above you 'knock off' point, which to my mind is 'waste' (expensive waste)
I think it is a very versatile heater so in my opinion it is a " GOOD BUY"
