Thanks for the replies folks, I ended up going with the same '18 Merida as @martyyn. Must admit I don't actually mind the lime stripes haha. Damn near died on the way home yesterday having to go up 2 rises due to a lack of physical fitness.
I went on Friday afternoon and tried the 2019 300 vs 500, and while the 500 felt a little bit nicer to ride, I'm not entirely confident that it wasn't just a case of perception bias. And certainly not $150 worth of difference (which went towards a nice Giro helmet and some good front + rear lights).
The other thing I noticed was the Manitou had a progressive lockout, but eh. If I find I make use of it enough, I'm sure it will easy enough to upgrade to above entry level kit in future.