I've used the same one in OP for about 8 months, not had any problems with it (fingers crossed) apart from the big bag like filter gets sucked in after a while. But I phoned the guy and he said just remove it and sent me some ready cut foam filters to put around the motors etc.
Power wise, it's gone through everything I've thrown at it - albeit mostly residential jobs but a few bigger commercial jobs. When I get more commercial work from it, I'd probably want something a bit more powerful etc.. just my two pence.
Also as I randomly found out Viper is owned by Nilfisk, if that means it's not bad quality?