To be honest I couldn't give you technical reasons as for why as I would just be copying things I have read elsewhere, which while I do understand them, I have no first hand experience to back it up. Both seem to have their positives and negatives but for me I am planning on having a new manifold made up next year to move the turbo (as of yet to be decided) to a top mount position and slightly over to the side so there won't be much space for the MAF sensor then, that and the fact that it was on the rollers a couple of weeks ago and apparently the Z32 MAF was close to maxing out, I am going to go with a Syvecs ecu regardless so it just makes sense for my situation to do away with it and use a MAP sensor. I am sure someone with more knowledge on these matters could enlighten us both here, I may even ask in the forum myself actually.
The Syvecs ecu is costly but does seem to be a really great piece of kit, from speaking with people and from what I have read they are very similar to a MoTec.