The last one (allowing us to manually change cartridge and store the partially filled one we have) would be useful. Can't say that the distance between samples is any kind of issue for me in and of itself.
Yeah the distance isn't an issue really, in the right area I just point the SRV in one direction and keep going, collecting samples as I go. The bacteria I always collect from the ship and don't use the SRV so that's not an issue. Limited cartridges seems strange, they are small and we could easily carry a few on us, swapping as we go, yes it would get a pain if there was no way to identify which was which and having to swap between them to find out which one to use, so I think two would be ideal.