Diy(ing) an air to air unit

[G and J]

We're struggling to get an upstairs fan coil solution (which was the original plan and piped for) that we're comfortable with, but in the intervening period since we've moved in (heatwaves etc) we're wondering if we should just go for a stand alone air conditioning unit.

 

Panasonic do a good looking r290 unit (solo) of the right spec, which looks straight forward enough to fit (annoying that it will be retro fit but there you go...) but

 

1. Is diy installation an reasonable option? and 

2. One supplier claims that unless professionally installed the warranty is invalid. Accurate or likely to be part of the sales pitch?

 

Views appreciated.

[LaChab]

Which unit are you thinking of? (Google failed me!)