I've been playing an electric guitar for 50 years with serious intent and this means I've played through many amps, many guitars and many pedals. I'm currently gigging with 3 different bands and play around 100 gigs a year. At this point in time I have arrived at a very basic set up for most of my gigs. 1 Amp head (Bluguitar amp 1), one 12" speaker and one pedal which is a Zoom multi stomp that I use mostly for reverb, delay and tuning. I'm very happy with my sound but the painful, pointed, directional result of one 12" speaker in a small room or on a small stage was always a problem.
We're always being told to turn down because the speaker is usually aimed at your legs (unless you raise it and possibly lose contact with the floor and thus some low end) and if you're raised on a stage it will be firing directly into someones ears or face, worse if it's the front of house sound person. You still might not hear it clearly unless you get it in your monitors. In small rooms, rehearsal situations etc, that's not always an option.
I know it seems expensive but I've paid the same or more for many a pedal that I'm apparently not using anymore. The Deeflex makes a difference. It might appear to be subtle but it really isn't. Very simply it does the obvious and corrects the aforementioned problem of the directional speaker cab. You've seen players turning their amps around, or opening hard shell cases in front of a speaker cab always to avoid this very thing.
Here is an accessory that solves that problem and I can't imagine not using it forever. It's allowed me to turn down a bit and for me and my band mates to hear a more pleasing version of my guitar tone. These things matter. You can tweak the eq to a fine degree but if it's still coming through one speaker cab it's going to be painfully bright and loud for someone in front of it. Not with a Deeflex.
What might be negatives? Well it's not that easy to pack but I took the cardboard box it came in, added a cheap plastic handle and covered the entire thing with black gaffers tape. The box can sit on top of a pile of gear in the back of the van without much issue. It's a minor annoyance in the grand scheme of things, especially when you find yourself on the floor in a tiny pub not mic'd through a PA. Then you're really glad you bought it.
Sonic brilliance is not always going to come in the form of electronics. Sometimes it's basic physics. Maybe you could make one cheaper but they've already made one, done all the research etc. There's all sorts of angles involved so it seems a hassle to try to fabricate one. I tell you my brother's and sisters in music, it's worth it, just pull the trigger and get one if you're convinced enough to be looking in the first place.