I'll echo rossmacd and say that seeing it's economy you should just go for the cheapest option.

I just booked flights this morning for a trip to NYC in December and decided just to book from Glasgow with BA - it worked out about £50-60 more
expensive than a BA ticket from INV but factoring in hassle and cost to position myself there and to have to get back to GLA after the flights it was a no brainer to just book from GLA.