Yes, I did. Sorry for not replying earlier - been running the MasterFuse in. I'm not the best at describing the differences in sound quality but I would say that the soundstage sounds more open and there is even more resolution of fine detail. It is even easier to follow the individual musical lines if you are inclined to, while the music seems to flow that bit better. Is it a subtle or a big upgrade? For me it's somewhere in between though now I have those changes I'd rather keep them. I was able to get a 10% discount on it and sold my SR Purple on eBay so it cost me about £400 overall. Yes, that's a lot of money but I'm not sure I could get those improvements any cheaper by changing my components. (Though see below!) So to answer my own question I would say it is a worthwhile upgrade.
However, now for a gripe about SR. As soon as I had bought the SR MasterFuse SR announced the introduction of a new 'Pink' fuse. If you read the description it sounds as if this is SR's new top performing fuse and yet it sells for less than half the price of the MasterFuse! (Pink £250 Master £595 UK prices) If that's the case where does that leave the MasterFuse? Will SR quietly withdraw it as their stocks run down? Also makes me wonder if I could have achieved the same results as using the Master for less than half the price. I'll be very interested to read any forthcoming comparisons between the performance of the two fuses.
I'll mention something which happened when I was checking which of my SR Purples looked the best (don't know if anyone else has had the printed part on the central bit of the fuse come loose? Doesn't affect the sound but it doesn't look good.) for sale on eBay I inadvertently put one back in the opposite direction to the others. When I came back to listen I found the sound was not quite right it sounded too rich, a bit slow and congested. Point being I was quite surprised that such a small mistake could have such a big (negative) impact on the SQ.
