Yeah, made sure mine said 1/4" - my (maybe incorrect), assumption is that the guys advertising 6mm and the such, are just being lazy with their descriptions?
Berkshire I'm afraid. The spiraling costs of my kitchen remodel have pushed me down this road, besides, the more savings I can make on the more easily accessible items, allows me to blow the bank when I want something difficult to get, and overpriced!
No, they are probably different specifications. For example, look at the OF1400 on the festool.co.uk site and the identical machine on the otherwise identical festool.de site. UK is listed with 1/4" and 1/2" and german site with 8mm & 12mm. My experience is that the UK tends to mainly use imperial sized bits (but not exclusively - we also seem to have 8mm commonly available) and much of Europe uses actual metric. The problem comes when you put a 6mm bit in a 1/4" collett (you will actually be hard pressed to do it the other way around) - they don't grip properly and can become dangerously loose.
A minor edit! I use two old Elu MOF96e machines with 1/4" collets, and also have an 8mm for them which is used with some specific long bits that were not available in 1/4". I have actually had a bit thrown - maybe not fully tight or possibly undersize and fortunately it did not hot me but flew around the workspace - could have been nasty.