I have a Blackstar HT5 I use for practice and rehearsals, I bought it with it's matching 1x12 cab, which uses a Blackstar branded speaker inside as standard. However I never really enjoyed the sound the amp gave me in this configuration and after playing through a Marshall Greenback cab I knew I needed some Greenback love in my life, so I chose to replace the crappy speaker in my Blackstar cab with this one. And since then I've never looked back.
This speaker has a lovely warm low end I enjoy, and even though I play metal, which you could say is very atypical of the typical user of this speaker, I actually have found it to be very capable of giving a nice tight metal tone, but still having that low end thump I love, which you get from Greenbacks. It's very hard to describe but after listening to many YouTube comparisons I felt this was the sound I wanted, I suggest you do the same as tone is very subjective after all.
Although I must stress that this is a very low wattage speaker, at 25w you will need to be careful what amp you hook up to it, also this means there's little clean headroom before you get speaker breakup, even my 5w Blackstar achieves this where it's original speaker was quite rigid in sound.
I have fallen in love with this speaker's sound and even though I play cranked a lot of the time I have had no issues with the speaker at all, and I've had it in that cab many months now. But then it is a Celestion and they are pure quality.
Great service from Thomann once again, and a great price too.