I bought a laser tools one off ebay for about £26
+ cheep
– no internal water tank so had to buy a water tank from halfords
– no battery so only works in the car
One thing I found helped a lot (and proobably applies to most cars and washers) was cutting the massively long power lead down to a couple of meters (just enough to reach the dashboard power socket) and only using the dashboard power not the boot socket. Doing those two things (especialy not using the boot socket) made a huge difference to the power.
The internal/external tank isn’t really a negative, and a 25l drinking water container is more usefull than a tiny little one built in, especialy on longer trips where it needs to wash more bikes or be drunk!