First of all, you can find a lot of info here by using the search term "Essex"; the Talk Bass search engine has trouble with two-character strings like "SX", so most people post about their experiences and/or questions by incorporating "Essex."
Anyway, I own three SX basses, and the key points are:
1) They use solid alder and ash for the bodies (which is good); the bodies (and neck pockets) are bigger than the industry standard Fender size, so you may or may not have a problem with swapping necks.
2) The hardware (in my experience) is perfectly functional; people do replace the string tree because it has slots underneath which have been known to hack away at strings -- you can also simply turn them 90 degrees to remedy the problem.
3) The pickups are nice and hot, but sometimes microphonic.
4) The fretwork is hit-and-miss; you can get a great one (and I have gotten two) or you can get one which needs fret levelling.
5) Don't expect boutique quality. You'll find quirky cosmetic defects (if you care about that stuff).
And finally, the big one:
6) I know you're in Canada, but I assume you'd be ordering from Rondo Music in New Hampshire? Their customer service is excellent, and if there is anything wrong with a bass (or even if you simply don't like it) they'll return it or replace it, no questions asked.