Schlagwerk CBT10 Cajon Bass Tube

Bought this for my Thomann CAS 100 cajon. Was trying to get more separation between the snare slap and bass, but what I actually got was a sound which works brilliantly where you need real punch to the bass, rather than a general 'boom' - Lol! Like anything made by Schlagwerk, it's a quality item. Seemed a little pricey for what is basically a plastic tube, but .... ya get what ya pay for.... Pros? Fitted perfectly in my cajon and the improvement in bass punch was immediate. Cons? tried this in my mates box and it was loose. Measured his sound hole and it was only 4mm (yep - just FOUR mm) larger and it was flopping around to the point where one slap on the front surface had it flying out the back! When they say 'for cajons with an APPROX 120mm sound hole' what it really seems is that MUST be 120mm!!
Other than that.... nothing really. It does what it does - and makes micing the box externally less problematic- a tighter mic pattern (even polar) can be used as the tube focusses the sound.