I've used it quite a few times (as I always do with any Scottish service to Knock!). From my experience the loads have varied from similar to the last time the service ran (40-50% of seats filled) to a major improvement (over 75% of seats filled).
The route definitely benefitted from the exploits of Connacht Rugby this year - Glasgow Warriors visited twice in successive weeks for important games in May, then Connacht played in the Pro 12 final in Edinburgh at the end of the month. This resulted in a lot of flights on the route being sold out by supporters around that time. I think the Glasgow team and coaching setup also used it for at least one of those trips.
The last time I flew the route (about three weeks ago) there were 67 on board heading for Edinburgh on a Monday evening. I doubt that is representative of an average load though, it was probably just a particularly busy day.
The main difference between this time and last time is that the route is now operating six days a week. I haven't had a reason to fly it on a Tuesday or Wednesday yet, but I suspect the improved weekend loads may be cancelled out by weaker midweek numbers. Of course the Brexit vote will not help inbound tourism this summer either.
It's a pity we don't have the CAA stats this year to get a better idea of how it is doing, although the CSO stats will eventually start to cover the months the service has operated.