I recently bought an HPF-Pre 3 from TB'er fdeck, and I wanted to give a quick review. You can read more from him here: https://sites.google.com/site/hpftechllc/
First off, I'm in a very loud band, and I've blown quite a few speakers. And in general, projecting clear and focused lows and low mids at high volumes using medium to high gain can be a challenge when using only an 8x10. (I use a GK2001RB and a variety of gain pedals and EQ's)
Another TB'er here recommended the HPF that fdeck makes. I believe fdeck is an upright player and the HPF-Pre is designed with that it mind, however, it has worked out great for my needs and I would suggest it to any heavy or loud player who wants to clean up his/her sound and make their drivers run more efficiently.
The bottom line is that your speakers expend a lot of wattage reproducing frequencies you can't really hear or need, and those frequencies create extra speaker movement that may be cluttering up your sound.
I put the HPF-Pre last in line of my pedals, set the Freq dial all the way down to 40Hz, it's range is 40-135Hz, and just pounded away at low E's, low D's, and low B's while my guitar player slowly turned the dial up. Right off the bat, as soon as I moved north of 40Hz, I could hear the tone slightly tighten, as I believe the speakers weren't working to pump out anything below 45Hz or so. Depending which bass and/or effects I was using I could hear some lows drop at maybe 60? maybe 70?, (maybe some frequency markings could be helpful here, but relying on your ears to find the sweet spot is probably the best practice anyway) but even still not necessarily a deal breaker for that type of music.
I think I settled in with it at around 50-55Hz, and it's made a pronounced difference in my sound, by itself, and in the band mix. For low B, I feel like I can be punchy and hard hitting without worrying that 30Hz is either blowing up a driver or sucking up wattage and driver accuracy.
Fdeck did express reluctance to me about claiming his product offered "speaker protection" so I couldn't say that it does perform that function directly, but if you're turning up, hitting harder, or adding high mids or more gain to be heard in a loud situation, you definitely more likely to cause speaker damage, as I and others can attest to firsthand.
Anyway, if you're having any of the above issues or just want to take a shot at cleaning up your sound, it has worked out well for me.