My normal advise would be: get hubcentric adaptors that bolt on, if you expose an additional 16mm of thread then the amount of stretch will increase massively and you will risk them working undone, especially if they get them hot breaking hard and then corner hard.
I guess if its a 1.2 for pottering to the shops and back though you will probably not have a problem, but its still nasty IMHO to do it that way.
I agree with chip there, that's spacer is rather large an I would certainly consider a hubcentric even though they are more expensive you can put a price on safety.
What sort of extra strain/load will these put on the hub/wheel bearing? That's one thing that had always put me off spacers.
What about handling? Would running a larger spacer especially up front effect the handling?
What it will normally do is improve stability when cornering hard on a fixed radius, but also introduce additional bump steer, it will also alter the ackerman characteristics slightly.
So basically what you get generally is, more grip (and hence higher ultimate corner speed) but worse handling (caused by bump steer and tramlining)
Different cars do react differently though, so in some cases its worth the trade off and in others it isnt.