I just discovered this. Are they any good? Would the v3 be better than the sporter?

I have one of the older ones.It works great for checking velocity on your rounds,but the point of impact does change so I don't use it when I'm shooting groups.One of the advantages it does give you is you can install it at the bench if your at a public range.I've compared my readings to my ProChono and they are very close.

I have a Pro Chrono and a Magneto Speed Sport.
I seldom use the Pro Chrono anymore since it is more hassle to set up and is subject to lighting interference.
I do use the Pro Chrono when I want to check down range velocities so it's nice to have both.
The magneto speed does shift POI so I use it after finding a promising load to verify velocity.

The sporter is easy to use.

It might mess with groups but it has not been by much.

We have not gotten out the tripod chrony for a while.

Really like mine it is the sport model. I am fixing up an independent rest for it to avoid any change in accuracy. They can slip on the barrel which will throw of a progression of shots but this has happened very often and some duct tape or the Caldwell mount will fix this.

I just bought the Sport a week or two ago. My old chrony died. I've used it on four rifles so far. It is super easy to use. Definitely plays with your POI. So far I'm very pleased and wish I'd bought one sooner. Can't speak to durability, obviously. If you get one, I hope you're as happy with it as I am with mine.