The only real issue that we normally experience is scaling when used on an open loop. In that case, we install isolation/purge valves like you would with a tankless water heater so it can be de-scaled.
You can choose to do what you want, but you cannot choose the consequences.
I use them quite often for commercial dhw production. We use the GEA heat exchangers and oversize them for lower temp boiler water to keep in condensing mode. Try to size boiler temp to dhw temp as close as is feasible for this.