I have also succumbed to the trend for tail tidies on the basis that the stock ones to a shite job, so why not make the bike look better.
It surely can't be that difficult (for the manufacturers) to design and engineer something that is not only visually more acceptable (crazy regs permitting) and also more effective.
p.s. I don't mind getting mucky occasionally, but I do think the front mudguard is more important as it would protect the engine (and rads)...unfortunately they are generally even less effective than the rear ones.