Personally, and I don't know what others think, but I would install some joists across the garage fixed to the bottom of the rafters to prevent potential roof spread, which looks to me like a risk. That's a shallow pitch roof and the outward forces are therefore going to be considerable when the roof is loaded. I don't think those short collars bolted high up are going to help much. I'm not a SE, but have a technical background, and it doesn't look right as is to me.
I'm not 100% sure, I've been assured its fine. there have been no signs during or after fitting tiles of any movement although I appreciate snow and wind could present significant loading. I may put some cross beams in at some point