School me on tankless water heaters please.

[Steve Maginnis]

I have a 4-plex, C property, 2/1, built in mid 60's on a slab with very little insulation.  They currently have 30 gallon low boy electric tank heaters located in the kitchen.  I'm thinking about making the move to electric tankless here, and would like some advice.  I used to have a large gas tankless in a home and loved it, but I've never used electric.  The property is two stories.  One shower, a washing machine, no dishwasher.  Only two sinks.  I anticipate max water flow demand to be around 4 GPM, with low flow fixtures installed.  That would be a shower and a sink, or washing machine.  

I'm trying to get by on the cheap, so am looking for budget models.  Problem is, there seems to be a lot of exaggeration in the marketing of these units.  Some advertise they will increase temperature 20 degrees over ambient at max flow rate.  Given 50 degree temp from the street(located in Charlotte, NC), that would mean they may have to shower in 70 degree water if the washing machine is also being used.  That will not work.  Units I've seen online advertise up to two showers and two sinks at once, which sounds like a no brainer.  Then I read reviews saying to expect half of that when it's really cold, which still may be okay, or maybe not.  A tank runs me $300-$400.  I'm looking for something under $350 for tankless.  Ecosmart seems to be a good budget brand, but it's more like $450.  I understand you get what you pay for, and I plan to retire with these apartments, but just going back on my own with my property management company, I need to be very cost conscious.  I don't mind upgrading later.  I just need something that will work well enough for the next tenant, and I won't get calls that the water did not stay hot for the entire shower.  

I found this model for example:

https://www.amazon.com/Electric-Tankless-ThermoPro...

And another:

https://www.amazon.com/Electric-Tankless-ECO180-Ce...

 Does anyone have any insight or tips on how to proceed with a purchase?  Thanks in advance.

Steve 

First Investor Realty & Management