There are some previous threads on the KSS 40.
It's an awesome saw, but I would not get one instead of a Kapex.
The KSS40 excels at being a portable crosscut saw with mitre capabilities. If you want absolute precision/accuracy and deeper than 1 1/4" cut, that's where it will come up short.
Plus, the Kapex gives you ease of repeatability, fences to customize, hold downs, etc.
I use the KSS40 for doing outside work when I don't want to haul a mitre saw or don't have power close by. And it's super handy to take to the work instead of taking the work to the saw. Fencing, decks, siding, basic trim.
I tried the KSS40 out on some flat cherry trim and gave up after the first couple mitres - I just wasn't precise enough with my method to get the angles I wanted. Kapex one in that instance - just had to haul it up 3 flights of stairs.
The crosscut fence on the KSS40 is awesome. The 90 lock is really 90. Unlike the HKC which I read complaints about it being 'kinda' 90. Also the adjustability to different angles is great. Came in super handy doing siding up into the eaves.
Oh, and the flexirail that comes with is super handy for cutting sheeting.
It also comes with an edge guide that works really well for doing rips(once I figured out the tricks to using it).
Long story short, KSS40 is a great, small portable crosscut saw.
The Kapex is a great, compound mitre saw.
Only you can decide which features you'd rather compromise on.