So with a B'day coming up next month I think I'll splurge on the Double 4 or perhaps the Cub BG100. It's small and light. I'm from the old days of a Fender Bassman so seeing something that small and light, I naturally balk thinking the PJ won't handle it.
That's usually the first thing people think/say when I walk into any gig setting with the Double Four; it can't handle it. Five minutes in, they're usually fine.
If it helps, I've used the Double Four in a theatre pit setting, in as large a group as 40 people and the soundman can always CLEARLY hear me through the mix.
Nearly every other manufacturer that makes a small practice amp offers it more out of convenience and an extension to their product line. Phil designed the whole thing from the ground up.
Any thoughts or suggestions on the D4, Bg100 or something else? I'll rarely play without it plugged in so will give the lithium battery a bit of thought. Will more than likely buy cause if I don't, I know circumstances will come up to where I'll need battery power.
I've had both, and also gig regularly with the PJB Briefcase (their "flagship" model for over a decade). The BG100 is very nice; it uses Phil's Neo speakers which give a more "traditional" tonal quality to the amp (in comparison to the Briefcase, which use the PJB Pirahna speakers). It also has two channels, the first of which also allows either a 1/4" or XLR cable, perfect for using with a double bass (channel one has a mic and channel two the pickup) or for vocals and bass. When I used the BG100, I used it to double between ukulele and bass and it works well; Phil's stuff is pretty full-range in terms of sound reproduction so you could easily plug any instrument you want into it and it would sound awesome. It's also got a handy "kickstand" on the underside of the amp, so you can tilt it up a bit to be heard as well as an actual DI out, if you're running to the front of house (the Double Four only has a 1/4" line out, which serves the same purpose but not as handy).
The Double Four however, was what made me sell the BG100. While yes, it's only 75w compared to 100w of the BG100, it's designed in such a way that I honestly couldn't tell a difference. The speakers are a third design, which I find marries the warmth of the Neos with the punch of the Pirahnas (this is probably why when I A/Bed them, it was hard to tell a volume difference). They both have the same 3 band EQ where the BG100 has a Limiteer you can also employ if you want. I don't personally need the option of the lithium ion battery, but it is very handy to have if you do need it.
At this point, I'd choose the Double Four out of the two, unless the extra options that the BG100 offers (2 channels, limiter, DI, kickstand) would fulfill your needs better.