I use this in my studio for recording, I have my ac 30 set on top of it.
The greatest advantage I have seen (felt actually) is that it got rid of the lower rumble that would spread across the floor when I crank the amp in the room. This makes up for 2 pros actually: less noise going through to the floor/walls and a clearer mic signal with less rumble when I put a condenser like the AKG414 to the speaker. I imagine someone in a home studio would get even more benefits from this.
The only downside for me (and this might be petty but I have nothing else to point out) is that it would be great if, in the future, they came in specific size for certain amps/cabs, or maybe rounded corners ('cos i've hit my shin against it a few times and it really hurts).
Overall I give it a five star review. For this price point It works extremely well and it definitely improves my recording situation and I will definitely be getting a few more of these in future for other amps.