I know that Turbo snails are very sensitive to ph changes, so I took pains to ensure the freshwater chemistry & temp was as close to my main tank as possible. The dip is only about 3 minutes, so the salinity sensitivity is not really an issue.
I got a dozen turbo snails and had no problems with the freshwater dip. Also several of them have been able to right themselves with no problem. Because of their shape, they never really go all the way upside down, though.
In any event, I think it's smart to observe your tank on regular basis, so if one does invert and can't get right itself, you can quick help.