The infinite probes thing jarred a bit when I first heard it but after five minutes of trying to come up with a rationalisation I just gave up and accepted it as a gameplay decision.
(FWIW the best retcon I could come up with was that when we enter a ring system our cargo or fuel scoops can be used to hoover up some of the larger bits of floating detritus in the dust, which contains enough trace metals and minerals to synthesise microprobes. Whenever probes run out, fly through a ring for sixty seconds. I guess FD could put something like this into the game -- it doesn't involve SRVs or mining lasers so it wouldn't require Horizons or a trip back to civilisation to re-equip -- but it would be a lot of effort to fill a gap in the lore. And it would require the probes to be made of a particular substance that's only found in the dust but not in the asteroids, which would add a brand new level of confusion to the whole materials / ores thing. Best leave it alone.)
As for the probes themselves, I though the visuals and the speed were just about right. They reminded me of photon torpedoes. I thought they were conducting Spock's funeral when they fired the first one. The fading effect on the "tail" seemed a bit off, but that might be a difficult effect to pull off and the graphics might not be optimised yet. They certainly looked better than the "comet tails" ships have when nearby in supercruise; they've always seemed very artificial to me.