Although I've played drums and percussion for more years than I care to even think about, this was my first Cajon.
Didn't want to spend a large amount for a first go, so bought a Thomann model as have found their own brand instruments to be good in the past.
With the CAS-100, you get what you pay for - and a bit more. Well-made for the price, it gives a good range of sounds, but lacks the 'polish' particularly in terms of sound quality of more expensive models. It's a full-sized Cajon (50cm high), and comes with two snares inside. A lot of players will slacken the front plate screws at the top to get a bit more snap to the snare sound. I tried this and ended up re-tightening the screws as I wasn't happy with the effect. Once put back to how it was out of the box, all was okay.
Given the price, you have to accept certain limitations, so it would be nice to see Thomann offer one particular bundle with this model - that is to include a Bass Tube (ie. Schlagwerk) as, to my ear, the bass is not too well defined and I think this would be a big improvement. Needless to say I'll be buying a bass tube on my next order....!
Best thing about buying a Thomann Cajon (even instead of a Millenium one!) is that you get a padded rucksack bag with it which saves you a bit of money and you have a bag if you upgrade at a later date.