Don't know about the Primos one also, but did by an LED light 2 yrs ago that has the blue "blood tracking: lense.
Got to use it for the first time last yr helping a buddy trail a doe he shot with blackpowder.

I say its 50/50 while the blood is fresh and still wet it helped switching back and forth from the blue to the white in spotting small drops ofblood on the leaves.

A few weeks later got to use it again as it started to sprinkle rain. The blue lense made it worse to see blood as every rain drop looked the same as blood.

I say to either buy a good bright white LED or get some CSI spray they use on crime scenes with a black light to make the blood glow.