I have been a dealer and user of MagnetoSpeed for the a few years, and have seen what works and what doesn't!
The above have pretty much all been addressed by this point in the V3. It has modes in the display unit to handle measuring full auto fire rate, pellet mode for air rifles and a mode to handle shotguns. Just recently MagnetoSpeed also released a rail adapter for the bayonet so it can be used with handguns that feature an integrated rail.
I have seen and handled all of the models MagnetoSpeed makes. I buy and sell used MagnetoSpeed models as well, and consequently see what works and what doesn't.
The V1 and the V2 shared most parts. The display units and bayonets can interconnect between the V1 and V2. Besides the difference in bayonet size, the primary distinguishing factor of the V2 is that it came in a nice plastic box and had spacers to allow shooting with a very large muzzle or a suppressor.
Initially when the V1 was released it had a plastic buckle setup which was replaced by the manufacturer because of the large number of complaints regarding broken and less durable buckles. The replacement buckle (also used on the V2) is a red anodized aluminum part which is very sturdy and had held up very well.
As an aside - MagnetoSpeed continues to offer the replacement buckle on their website for owners of the V1's with the original plastic buckle. If you use the coupon code "click" you can get a nice discount when ordering this from MagnetoSpeed.
The primary reasons to buy the V2 was shooting a rifle with very large muzzle, shooting with a suppressor (aka silencer) or shooting a rifle with a very large (or long) muzzle attachment like a brake or flash suppressor.
Overall the V3 is a significant improvement over the V2. If you already have the V2 should you upgrade? You will have to decide for yourself if the upgrade is worth the value of all the new features in the V3.
I still purchase used V2 models and offer a unique trade-in program towards the V3. If you are interested in upgrading - feel free to contact me for more details.
A final note on all the MagnetoSpeed Chonographs:
Some people like to hand-load ammunition. Some of the people who do this reloading like to develop loads while at the same time working on zeroing (where the center of the fired group is located). On some rifles attaching the bayonet to the rifle barrel can cause a point of impact shift. This is mostly seen on thin profile barrels. The bayonet weighs 5 oz - so is very light and has negligible impact on heavy - particularly short heavy barrels. Group size has not been seen to be affected by attaching the bayonet to the barrel - however if you are worried about this, the very simple solution is to perform load development without the chronograph. Once you find a load that groups very well then verify the muzzle velocity. Make sure you are checking for pressure signs on your brass - which is something any reloader should always be looking for anyway.