I've not heard either but the two chaps in Hi fi gear in gloucester UK were talking at length about these two brands yesterday. One has Sunfire, one has M&K. Both seemed very happy with the subs. Find them online and give them a bell or email ... super helpful imo
If you want to get a lot of bass from a small box, the Sunfire is ideal. But for me, and for those who can house the much bigger cabinet, the SB1250 will be the better bet. Fast, punchy, and sounds 'big'.
The HRS10 might be 1000 watts on paper, but it all depends on the frequencies being produced by the sub, and therefore the travel of the bass driver that will limit it's output. The bigger the bass driver, the louder and deeper at can go. Don't assume that a more powerful sub will go louder, as many other factors will come into play.
Even though the SB1250 is 250 watts, I doubt very much that many people would reach even that sort of power in the average living room, let alone 1000.