Yes it was worth it to me
Have the tank about half full in the morning (about 90 litres) and run the immersion for an hour normally.
Get to the first job and first thing i do if i want the water hot is plug in the immersion while i vac etc. If i am doing a few rooms by the time its all prepp'd the water is nice and hot. You have to be careful as its like any immersion tank - the water will get hotter towards the top first so you can mix it round if you want to even it up but because i drop the tails from the Airflex into the tank, the Airflex mixes the water up as it dumps it back into the tank with the pump running.
I did a 3 piece suite and carpet last week - plugged it in when i got there, vacced the suite and carpets by which time the water was a good temp. Then rinsed through the suite and plugged the immersion back in while presprayed carpet and again water was hot - hot enough to make the brass connectors hot.
You arent going to get scalding hot water from it - but it does help and is better than stone cold water rinsing from a tank in the van in winter.
The insulating of the tank makes a huge difference - i used some immersion tank insulation from Wickes - made a massive difference in retaining the heat and speeds up heating as you arent losing so much energy in the cold van.
You need to be organised - being able to drop the pipes in the tank from the Airflex helps a lot - no filling up of the machine at all - just dumping which is normally done at a break in the cleaning any way.
I've had no electrics tripping with it and the cables arent hot at all - they are hotter on the Airflex when thats been used.
Its helped me thats all i can say!!