Maybe, but the MOT test only checks for a minimium amouint of light, general alignment and any difference in colour from one headlight to another - it does not cover excessive overall light, glare or colour per se. You could fit 120W purplish bulbs in a stock headlight and you'd pass an MOT. That doesn't make them legal.
The wild claims for uprated bulbs are not so wild, they are just misinterpreted - +50 / 80 / 90% bulbs do work, but they only produce that extra light at certain point of the beam pattern. If a standrd bulb barely stretches to 100m distance, its not difficultt to claim +80%. Ditto with a dark spot in a beam pattern.
Fitting any HID kit or conversion means you run the risk of invalidating your warranty (certainly for any electrical system failure), invalidating your insurance and getting stopped by the rozzers (although thats highly unlikely seen as they take no notice of the 20% of cars driving around with one headlight or using fog lights incorrectly).
Down to personal choice and your approach to risk.
