The benefit of the hybrid (which has a 40 gallon tank) is that it only requires a 1/2" gas connection, which is what we have. We can't go tankless because we would have to replace the gas line out to the municipal supply at the street, which would be cost-prohibitive.
We've been in the house for less than 3 years and are not sure how well the prior owner maintained the unit. We are pretty handy but this is our first house and we just learned about the yearly sediment flush - so we haven't been doing that. We have a baby on the way and I guess we're thinking about a preemptive replacement since we're not sure of the condition of our current unit and don't want to deal with the possibility of an emergency replacement with a newborn (and a finished basement, by the way).
We seem to have enough water out of our 50 gallon unit for our own day-to-day use, but we do run out when we have house guests, which is fairly often. My in-laws brought their camper instead of staying with us on their last visit, partially for this reason.
I'm not sure we know the "true lifespan" because I think they are a fairly new product.
We did find this unit on Lowe's website and it looks as if our new guy is quoting an additional $2100 to install it. Probably more, since I assume he can get it at a wholesale price. I think perhaps we are being taken for a ride...
At least he didn't charge us anything for the A/C troubleshooting, but his associate put seven holes in our drywall trying to find the broken duct. I am so sick of dealing with service people.