Phil Jones Double Four: I bought one. Sent it back.
I use a Gk Micro Cube 150 watt 12" combo with 12" extension cab for loud upright, U-Bass, and even electric bass work.
Friend built a remote power supply where I can use DC too.
For real light work, I use the Roland Micro Cube Bass RX. Needs to be backed against a wall to get head room.
I also use a Polyntone 15" for upright and U-Bass really works well for it too.
Sorry....I think that Phil Jones Double Four is overpriced, the battery add is a hassle, they lack headroom - their suitcase amps are good.
My opinion for what it is worth. I have been a bass player since 1968 and seen every and/or owned many gyrations of uprights, electric basses, and now these U-Basses