Nice but a tad too late. I've already ordered a Joven 35L.

Mine over the roof is exposed and then to the bathroom is concealed. What are you trying to find out?

This is a tough one! I too have similar problem, and was contemplating if I want to fit a instant heater.
I have a storage tank that feeds to my tub, sink and a shower. The pipe that goes to shower is block, the plumber tried various way, to clear the block, but nothing worked.

Finally decide to stopo using the shower area, since I have a tub which can also be used as shower and 2 other bathrooms.

In your case, you may look into, not hacking the wall, but re-piping on surface with casing, that will help for future repair works and doesnt look that bad.

And yes, the other option is to fit instant heater
Personally, I dont there is a THE brand, it depends on what you want and the look/design of it, which is very much individual liking. If you want lesser noise, look for DC motor types, and if you dont mind noise, then AC motor has a little bit more power. Long time ago, the gap of the water pressure was higher, but nowadays, its much closer.

Look at the energy rating and warranty as well. Personally I like Alpha, but there are many more new players in the market like Deka, etc, do check those out.

This is example of mine ...wanted to do casing for my wiring, just havent had the time yet.
[attachmentid=11513615]

The casing is PVC and not metal.
The shower rod is metal, and my whole unit is 20 years old, no rust thus far. Previously my family had Pana, and switched to Beebest back then, which is similar to Aplha.
The valve, been working smoothly for 20 yrs. 

I went with this model, since it has both temp and pump controller. Back then not many models has pump controller.

yes half inch stop valve, but I dont use that, its only just in case if I need to work on the water heater to stop the incoming water. The water heater itself had a on/off valve, which its used daily. The vale is firm, no movements.

My area, during the day the pressure is lesser, hence with ramp up the pressure using the pump controller and at night the pressure is high and my parents doesn't  like high pressure, iso its helpful to control the water pressure, when needed.

Whichever valves u use to control the incoming water, make sure to also install the stop valve that comes with the instant water heater, as it usually have a filter mesh to prevent dirt and particles from entering the instant water heater and causing damages internally.
Dry burn will only occur if u didn't let water run thru the instant water heater before switching it on for the first time when the heating element tank does not have any water inside, hence the heating element is heating up air, causing dry burn. Once u let water run thru the instant water heater for the first time, there will always be water remains in the heating element tank as long as u do not dismantle the water heater (eg. for servicing, and the water inside the heating element tank is poured out), and the heating element will not be heating up air since there's always water inside (unless the heating element tank is leaking due to defects), hence dry burn will most likely not happened.