I hope you see this, lots of times when threads go 5+ pages, the later posts are paid less attention....
I have an M81 and it's great. Speaking strictly from the aspect of a DI, Over the years I've auditioned and used:
Ampeg SCR-DI (twice) sold both
Too boomy and just wasn't my thing. Sorry Jimmy, I tried!
MXR M80 (bought it on a Friday, returned it on the following Monday)
The OD is just not pleasant in my humble opinion. I don't use much, but I couldn't ever dial up something that made me happy...
Pigtronix Bass Station (yea it has a DI) They don't make them any longer but they pop here, reverb etc. They have a good info-only page on them at
Sweetwater.com
Sold mine in one of those grass is greener moments. Big footprint, but great! Honestly if I had it still, I'd have it, a tuner, and a bass EQ pedal in the loop section and be done.
Tech 21 Para-DI (twice) have the second one currently
It's my backup. Was my primary until recently.
MXR M81 (twice) kept the one I have and am using currently.
Switched to this one. Feels like home. Was prompted to put the M81 back into action because it has an adjustable input. When I play for my church, different bassists with different basses play and If I play a Sunday following someone with a weak bass signal, I need to be able to dial my bass back a bit. I know that should be done at the mixing console, but it's church. Volunteers are often absent, or don't notice, or don't know what to do...
The M81 is great as far as being a solid performer. It gives you subtle and very usable tone shaping. I've always found it to be a very forgiving DI when it comes to playing nice with your instrument. I have had basses didn't quite have the grounding squared away the way it should be My M81 always provided minimal hum despite my bass. I mean, not terrible hum, but there. I recall one having something not quite right with the series-parallel-single coil toggle. Another had a preamp that was a little noisy... Also, the M81 has in input and an output pot. I play church bass, and the overall mix is a real moving target. Having that control is a giant help when it comes to dialing in something you can use in deference to inexperienced or even absent sound mixing person. Overall it's just a great, quiet, reliable little DI.
I like my Tech 21 Para DI very much as well. It lives in my gig bag as an in the event of catastrophic failure backup. I figure with the blend-able in-built OD, sweep mids, and other buttons that it has, it's a keeper and could run the whole show if it came down to it. - Wouldn't exactly be my sound, but could get darn close with it and it's small size is hardly a problem to have it as a backup.
So that's my story, and am imagining that you are in close to the same boat from my read of the your OP. Hope this helps!