Great article, just to add / mention:
Most of these are not avail in MX, and are priced higher than MX models.
The electric ones also draw more power than many MX homes have available....
Best ones in MX currently in our experience are either Bosch, or the new redesigned Kruger units, which now work very well with and as an automatic backup to solar hot water, and are very well priced. Fast, continuous, & seamless (good performance with or without sun) hot water, with the minimum of gas use. And isn't that really the goal? ;-)