It all depends on if you want infinite adjustment, or just a few specific setpoints. The black inline flow controls are nicer but unless you're out riding with an instant read thermometer stuck in the pisser you're not going to take advantage of that infinite adjustability. The other thing with the black inline ones is that there's no reference. If you want a spring and summer setting, you've got to trust the number of turns open, or bench test the flow rate each time to get it perfect. The other style you just pluck out a jet and put in a different one.
Oh, and the left pic: that's just a Colder Products fitting. I think that pic is the APC style. Without a valve (valve seals it when disconnected, not needed for water line), the white / grey button side is only $1.48. You can likely save some coin if you go to
www.colder.com and spec it out yourself. You might need to drill the insert side to fit a jet, I'm not sure.
A third, and even cheaper option, is to go to the specialty fastener bins at Home Depot and get some white plastic stand-offs, I think they're 1/2" long or so with a darn near 4mm thru-hole in them. If that diameter works for you, you just cram that in the water line right at the pisser.