As a guy that runs 80 InReaches for my work I would caution you to get a replacement fund started. The battery in the unit is only good for 5 years but I am seeing less life out of a hard used unit. Most of my units are 3 years old and I am starting to see button and battery issues, my personal unit is also 3 years old with no issues but it doesn't get used as hard as the work ones. You have to think that each new person that rents your unit is going to have to play around with it trying to figure things out plus the field use is going to wear the unit more then normal.
The unit is easy to loan as you can switch users and create a new profile for each renter so they only see there info and no one else's, it will require some data entry on your part setting up the unit for each user. Make sure you figure out what you need for contacts from each renter so you have all the info needed to enter.
Not to be a downer but you do realize that renting your unit will probably cost you more money in the end. Eventually your going to rent it to that one guy that loses it, doesn't pay or cracks the screen and leaves you holding the bag.