I've been hot for a while now & have tried a few DIY gas heaters.
I started with an Arazbao JSD20. Its a decent heater but too powerful, even on minimum heat I was worried about cracking glass on frosty days.
Next I went for an L5,.. much better heat range, I got one without the 20 minute timer, but it required a high flow rate to fire up (about 2.2 litres per minute) The L5 didn't die, just got replaced.
Next I got an Ammonstar heater (I got a 6L one, but there are 8L ones on ebay). This heater looks quite pretty (stainless steel) and has a digital temp gauge on the front, but despite the sellers claims, it is not available without the 20 minute timer. My ammonstar heater died after 8 months due to the ignition unit melting,.. a MAJOR design flaw that could prove dangerous IMO. I'd never recommend one again.
Now I have a Fogwash. It doesn't have a 20 minute timer (good), it doesn't require modification to run at lower flow rates, it has a very good heat range & it is CE marked. Its also easy to fit a flue to it (unlike the L5 units). It is the best heater I've used so far by a long way. The only downside is that its a bit ugly. :