The HMEC25KA is not so useful in piston aeroplanes unless they are pressurised. The concept of these headsets which sit on the ears rather than over them does not give enough passive noise reduction.
The most comfortable by far are the Bose X headsets which unfortunately are also the most expensive ones. They used to be nearly £1k but with some shopping around can be had for around £750.
Equally as good to my ears but a bit higher in clamping force are the DC 10-13 ENC (ANR) sets and depending on what model exactly you can have one of those for around £450-500.
I think that you will end up with 2 headsets as I don't think that any of them work well enough in both piston aeroplanes and the flightdecks of bigger machines.
If you don't want to spend too much and have a small head you may want to consider the DC 10-13.4 Y which is a bit smaller. They are a passive set only but cost a lot less at around £199.
Most important thing is that the set is comfy for you. So try them for a little while before forking out the dosh
FD