Looks like no one in that company actually knows anything about plumbing  I assume a brand cylinder unknown to anyone..

Am I covered if my tank needs to be serviced or replaced?

Yes, with Re:Heat the hot water unit is covered for as long as you are with us. We are committed to ensure your tank is working properly and we will repair or replace the unit at no cost to you.

I would love to read the fine print in regards to what this is subject to.

Is there a minimum term, what if I want to cancel the rental?

You can cancel the rental at any time by buying the water heater from us according to our buy-out schedule. After seven years you can cancel the agreement and would no longer be required to purchase the hot water heater from us. In this case you will be subject to an account closure fee along with a drain and disconnect fee if you want us to drain and disconnect it for you, a pickup fee if you want us to pick it up instead of you returning it to us and a visual inspection fee.

 -"according to our buy-out schedule"
- "subject to an account closure fee"

Bit fishy.. Maybe that's what happens when you sell the house.