It has no effect, if you never used it you can't say it does, I have shot 1/4 MOA groups with it without issue. It has no adverse effects on accuracy at all and only on some barrels have I seen it move everything up.
It never misses a shot, is not dependent on the light conditions and it's been put against chronographs that cost 3x more and the results speak for themselves.
I have an Oehler 35P, PVM-21, CED M3, SuperChrono and the MagnetoSpeed, it's the go too unit without a doubt.
It works, I use it indoor and out, in fact I use it on every students gun in every local class I teach.