I certainly won't make my money back in the cost to re-key after tenants, so I'm with you there. But it's 80 miles and a two hour trip every time I have to drive there, so it has saved me a lot of time and mileage. In this case I'll pay extra for the time savings and convenience.
Yeah, I suppose if you're sufficiently far away (and/or you have a lot of tenant turnover), it would be helpful.
Either way you have to go out there to delete/change the code though.
What we ended up doing is leaving the one mechanical lock on our first rental, and we have the second - whenever one of our rentals has someone move out (or we get a new house) we pop that on while people will be there replacing carpet, painting, showing the house to potential tenants, etc. Then, when they move in, we pop it back off for a regular lock and save it for the next house.
Once a renter is there, you don't really need it on (the tenant will need to be there to meet any handymen or anything anyways, so it's not needed for that), and so you shouldn't need it for that house again for a year or two.
When we have more than one house in that situation, though, we just use a regular combination lockbox on the other houses.