Bubble balancers

[Wait Here Until Green Light Shows]

Anyone here used one (I mean actually used or own one and can give an honest opinion, not Googled for answers which I can do myself). They seem more popular in the 'States but they don't often drive as fast as us so might not get much wobble at speed.
I tend to fit my own tyres and I'm thinking about getting one for the final step that usually involves spending money.