Yes I am interested too. I have done some research on this and other forums as well as asking about feedback in a few shops. Out of Coleman and Companion, the conclusion I came too is. And, yes. I know you can use a billy too!!!
1)The Aquacube Mark 1 had a lot of problems with the over temp sensor being too aggressive.
2)The Aquacube mark 2, ie the current one, seemed to fix this.
3)Many of the Coleman units have a lot of problems with ignition restarting and impeller failure.
4)Coleman is good for 70 degrees, but Aquacube is only 50ish degrees unless you remove the over temp sensor then it is about 60.
5)The Coleman is hard to regulate the temperature for showers and can go hot / cold if you stop / start.
6)Coleman is super sensitive to any impurities in the water, rendering it unusable.
7)Coleman has an internal 6V battery making it more portable, but it can be a pain to keep charged.
We have a Coleman and have it for about two years, the following are my observations in response to your comments
3)The only time I have had ignition problems was when the unit got left out overnight and was covered with condensation in the morning, once it dried out properly it was fine.
5) I would agree that for showering the coleman is not ideal, ours runs off the gas bottles on the front of the camper and if you only have a limited supply of water then turning it on/off continuosly whilst trying to keep it dry is a PITA. For that reason we use it to heat a bucket of water and then use a 12v shower. The hose that coleman supply to run it off LPG bottles is only 1.2m or so long, so if your gas bottle is plumbed in to the camper then where you use it for showers is limited to being within reach of the gas bottles.
6) We have only ever put river water through ours and have never had any problems with the impellor not working.
7) We easily get four or five days out of the battery and when it needs charging, just plug it into the camper overnight. Only problem is that you cannot charge the unit and use it at the same time, or once the voltage gets too low it will not ignite.
We only use ours for heating water for showers and for washing the dishes.