I had a little giant propane heater and loved it, they can get your water hotter then you need it. I never turned mine up much past the warm setting on the dial.
You do have to light the pilot light each time and you do have an added expense of buying propane all the time
I bought a new TM that uses a heat exchanger.
I don't think my HE can get as hot as the little giant i had but i never turned the little giant up to high anyway
The HE gets plenty hot enough and heats the water up really fast
I don't have to buy propane anymore which saves me money
I don't have to re light a pilot light at each job anymore
it just one less thing to worry about
I'm more then happy with the HE over the little giant
The only issue i had was my TM would dump water into my recovery tank automatically if you weren't using the wand. Machine wasn't doing anything wrong this is how it was designed.
I also have a 70 gallon fresh water tank so one time when i took it in for service i had the guy reroute where the machine dumped the water, so now it dumps into the fresh water tank and i no longer have too worry about my waste tank filling up to quick.
So after a job or two if the fresh water tank has a lot of water in it i'll just use it at my next job so it doesn't go to waste. If i need to dump it i'll just let it drain where ever i'm at as its just fresh clean water