The split DIY systems are easy fit.

Just remember they are precharged for a specific length limit, and on
many systems you can not shorten the hose - you therefore have to coil
it behind the unit either inside or outside. Might be useful to
investigate if various lengths are available.

For domestic, I've never understood why they don't do an "all outside"
system. Where there is just a vent in the wall with an IR window for
the controller - you simply have it blowing cold air in or hot air in
depending on heat pump mode. No hoses to muck about with re kinking,
no seals to go bad, no installation hassle or finding free wall space
and so on. Instead they do "everything inside, just two vents outside"
at a huge increase in price, often reduced CoP and whacking great big
box inside.

Another note is Invertor systems are a bit more efficient.