I know how hard it can be parting with hard earned cash, and there is definitely a gap in the market for some more detailed reviews. I'm going to try and review a product every week, so keep checking in.
I hope this is helpful, please comment etc. and please don't hesitate to ask any questions.
My first impressions of this stem were that it seemed impressively light, in fact it is so light that I thought it might not be strong enough! I was also delighted when I realised that it can be inverted so that the stems rise could be used (upside down) to lower the stack height, this was very helpful to me because I haven't gotten around to cutting my steerer tube.
Whilst riding with the stem I felt no noticeable flex, however I did manage to move the stem during a crash, this caused the headset to decompress forcing me to un-tighten and refit the stem. This may however be down to human error, I do not possess a torque wrench, so it is possible that I may not have tightened the steerer tube clamp correctly. It is also important to re-affirm that my steerer tube is of an undesirable length and this may have caused the problem.
Jedd's conclusion: The lightness of this stem really is astounding, it looks great and seems really nice and stiff, the ability to invert the stem is also a great feature! I'm sure that my issues with this product have were caused by human error, so just buy it, for £29.99 you cannot beat it! Well done to the On-One Crew!