I used to use needle valves, but had a couple problems with little bits of dirt getting stuck in them and reducing the flow, resulting in frozen bays. I switched it to use a watts pressure regulator to control the flow/volume. Pressure gauges allow me to see weep status at a glance. Also I split it to 2 circuits because I need more flow to the 2 furthest bays to prevent freezing. Also when I switch to hot water weep I want less water weeping, the regulator & gauge setup make that easier for me to do..
Yes, yes, I know, "dirt"... I use recycled weep water with a foot valve, these were small enough particles that they passed through everything except the needle valves. Not a lot, not real often, but frozen bays are not happy days. I did add a particle filter, I'm sure that would have been enough, but I like my current setup better. Works for me anyway.