I have had both a DLV backbox and now a backbox delete, my thoughts on both . . .
Late last year I went to see Mike at his home address to get one of his modified backboxes fitted, on Mike's advice I went for his standard modified box, ie at the quieter end of the scale. If you're after a relatively OEM sound at start up and lower revs this is the box to have, only in the upper rev range was it noticeably different with a few muted pops and bangs on the overrun thrown in for good measure. If you live on a quiet street and care about your neighbours then this is probably the best compromise especially if you're using your car for work everyday. However I was left wanting more, Mike did say if I wasn't happy he'd swap it for one of his louder boxes but for whatever reason at Mike's end this hasn't happened.
This week I have had a backbox delete done and boy oh boy this is what I wanted

From start up right through the rev range it sounds epic, popping and banging on the overrun and snarling and growling under acceleration. I was concerned it would be too loud but it just sounds right to my ears, I've listened to YouTube videos where they do sound too much but I can only put it down to poor quality recording equipment. I like it so much I've put all the foam back in the sound generator and I'm constantly wanting to get it out of the garage for a blast lol.
My advice would be to think what you want from your car and how you use it and ask Mike to do it accordingly as I'm sure he could make it sound like a backbox delete and pretty much any variation in between but for me backbox delete all the way
This is no criticism of Mike by the way I know he was busy with his new business venture at the time.