I have an old DOD direct box and a LiveWire direct box that I use for recording bass and sometimes a DI track for guitars. Nothing sexy about them. They do what a DI should do. I also see the Radial DI's and such selling for major dollars and scratch my head wondering what justifies that cost? The more I experiment with bass sounds in the studio the more I find a clean DI track from either DI being an important piece in getting a killer sounding track. I am truly not understanding what I am paying for in those more expensive units.
You are paying for the Jensen transformer in the JDIs. The box is pretty rugged, too. Their Pro line uses non-Jensen transformers, but they are still decent units. I own 3 Radials...2 JDIs and a stereo version of the JDI. I like what Jensen transformers do. Jensens and Lundhals handle really high bass levels better than the cheaper transformers. Having said all of that, if you are happy with those two units, then use them and quit worrying about what justifies the cost. If you are happy with your units, then carry on. Nothing to worry about. (I also bought a little Livewire DI that stays on my practice desk. It actually sounds very good. It's a fantastic deal, too)
If they're working for you, fine, but if you ever heard an expensive one side by side with a cheap one, you'd understand.