Most of these fittings are the same, only color and plating as well as finish and o-ring differs. In other words, theres no point buying bitspower when you can get cheaper. I use phobya/xspc/alphacool/no-name ones, because they cost less, the availability is good and there are many variations of fittings.
It's possible they could be saving some cost by using a slightly lower quality metal and slightly lower quality o-rings; it would be interesting to test that. Although I'm sure BP also have a healthy markup which leaves a lot of room for undercutting.
In the US the best deals on Barrow fittings seems to be PCCoolings and the-bestdealmarket, both are ebay sellers (tbh I believe both are actually the same seller - both based in Houston TX). I recently ordered a whole bunch of the fittings through them. I really like the matte black color a lot better than Bitspower's glossy, and the fact they don't have BP's logos all over them is even more of a plus.