I bought a Roland 'Ultimate Blues Tone Capsule' to go into my Roland Blues Cube Artist. It's a 1x12 combo amp with variable output power modes at 5w, 15w, 45w and 80w. You get the best out of most valve or valve-mimic amps in terms of tone, distortion and overdrive if you crank up the volume over (at least) half way. The variable outputs on a blues cube mean you can do this at the lower power levels and get a similar response with less noise production, but it is worth saying that at the lower outputs this works less well than at the higher ones! Of course the volume control on the guitar provides another variable.
Actually the amp sounds great without the capsule so why bother? Well, if you can get something that improves an already excellent piece of hardware then you probably would. I therefore spent some time looking at the various capsule options via online reviews and demos and opted for this one; mainly because I just liked the changes in tone and delivery that this one offered against the others - and it was a sound I preferred slightly to the original. But this is such a personal thing, please check out the options for yourself before you make the final decision.
It works well at all of the power modes and you can tell the difference, even at lower volumes. It is very easy to install, is small and tucks away neatly under the amp and is well protected from bumps and possible damage.
The bottom line is that it does change the tone and 'feel' towards a sound that I prefer - and for me that makes it worth it.