D’mand or Aquamotion for faster hot water questions: – GreenBuildingAdvisor

We have new construction slab on grade with in floor heat.  Our kitchen will have over 50’ of pex connected to 150,000 BTU tankless on demand hot water combo boiler system and almost 40’ to furtherest bathroom and pantry next to it. 

We do NOT want a continuous hot water circulation pump.  I researched and found a company that said we would need a D’mand ACT 1 or a  Aquamotion AMH2k-r.  The plumber looked at the website and thinks we will only have issues with only a 5 yr warranty.  He doesn’t think it will really work that well and our HVAC company should have installed a 200,000 BTU unit instead.    He is not thrilled at running a separate cold water return line so we only need 1 unit.  

We lived in 2 story newer home and it took over 2 mins with the over 50’ run to get hot water to upstairs and the water cooled very quickly when you went back 10 mins later.  This is why we are trying to fix this problem now.  

Questions: 

1. Anyone with real life experience with either unit or you do recommend other units to compare with?
2. How long is your water line run and does it really flush fast to get you hot water faster?
3. How long have you had it and had any issues?  
4. Do you have well water?  (Ours will be well water softened)
5. Would it be worth putting insulation on the hot water pex line to keep it hot longer?