A 199KBTU/hr gas fired tankless is great if you have a huge soaking tub or spa to fill! Most electric versions have limited output, and even then you'd need a dedicated 100A 240V service for the electric tankless to have decent tub-filling times for standard sized tubs at northern CA incoming water temps. (It matters!)
The cost of heating water with resistance electricity is usually substantially more than heating with gas too- comparable to heating water with propane, but it just depends.
The ignition delay on some gas fired water heaters can be an annoyance, especially in cold-water country, since a slug of water gets by the heat exchanger unheated on successive draws so you end up adjusting then re-adjusting the mix at the tap a couple of times per draw. (google the phrase "cold water sandwich" ).
They don't take up much space, the output and efficiency is good, but only the highest-volume users would ever make up the difference from a financial point of view at current natural gas pricing. In hard water country it's often necessary to de-scale the heat exchanger annually- not tough to do if you plan (and plumb ports) for it, but it's a maintenance issue you don't have with a tank, and if you're paying somebody to do it the economics of the higher efficiency flat out fail.
The (not such a bad) compromise position is to go with a 40-50 gallon condensing gas fired tank, which is simpler, typically doesn't require upgraded gas plumbing diameters or an upgraded gas service (if you go with a 76KBTU/hr Vertex rather than the largest-burner Polaris), and still puts out way more first-hour gallons than any atmospheric-drafted gas water heater of comparable size (or burner size.)
I'm neither a fan of, nor do I despise gas-fired tankless, but when I replaced my heating system boiler I went with a different approach retiring my tankless early (only 14-15 years of service- might have gone another decade), using the heating system to heat my hot water. I'll still never run out of hot water in showering mode (an important consideration for my family- YMMV), but it's only so-so on tub filling times compared to a tankless. As configured the new approach improves the space heating efficiency of my now micro-zone house, which was a primary reason for the change- the tankless was doing just fine as a water heater, despite having temperature control issues at very low flow. (If low flow temp control is important to you, look for smaller minimum-BTU numbers for any given model, and stick to Noritz or Rinnai, either of which have better than average temp control even at min-fire.)