Gas Models may require additional piping. So say if you have a storage tank hot water system, there may be a need to re-route a gas line or have a new one installed. This can lead to additional cost and work, which makes the price of the initial setup add a few extra $$. Keep in mind that a gas system will need to be piped in regardless of the presence of a tank, but because tankless systems are often wall mounted, more copper is required. If your gas line is too small, you may need it to be upgraded, see, continuous flow systems need a lot more gas to get that cold water hot fast and if you have a small line going to your tank, we may need to upsize it. Cost will depend on how far the gas meter is to the unit.

They call it instant but… its just a tiny bit less instant than a water tank

These units are not “instant” per say, they do take 2-3 seconds longer than traditional hot water storage tanks because you have to understand it has to get cold water to hot really really fast, but I think that is a good compromise. The only reason why storage tanks are more instant, is because they are always hot because they are always using your $$ to keep them hot. And remember this is not really a con, you will save more money on energy and 2-3 is not long, if you look at a clock and watch 3 seconds go past it is almost instantly, hmm.