Hello,
I currently did own a Fender Rumble 500 watt, it was a awesome bass combo amp, loud and fun to play.
But I did try out the Blackstar unity 250 watt bass combo and it was amazing! It is just as loud as the Fender rumble 500 watt. I decided to sell my fender 500 watt combo amp and go with the Blackstar Unity 250 watt combo bass amp, it is amazing, the low sounds and the distortion is amazing with all the setting, anything sound you can think of this bass amp will do it. My bass guitar is a Warwick fortress with MEC pickups and it sounds simply amazing, I have a few bass guitars but I love my Warwick the best. My advice, go with the Blackstar 250.
I Play old metal, Metallica, Motorhead, Slip Knot, etc....
I am actually going to sell my blackstar 250 and upgrade to the blackstar unity 500 watt combo. I hope this advice helps.