If the water is circulating through the coil, it is unlikely to boil to steam. Unless you do not have large enough of a tempering tank. or haven't used any hot water for a long time, you should not have an issue.
If no hot water has been used for a long time, then just run some hot water to cool down the holding tank.
If plumbed correctly you should have no problems.
As for insurance, if the plumbing is done to code they should not be able to deny coverage.
As for being worth it, personally I like not burning ANY propane to heat the house and water. It's worth it for me. The only propane I burn during winter is for the clothes dryer and cooking. Maybe $20-30/month. Much better than the $1200++/month before coal.
Hope this helps. Greg L.