In my opinion, none. The manufacturer claims you need a license to connect it to a wideband (Zietronix, Innovate, ETC.) but that's false info.

I've connected my Innovate wideband to it and it reads the A/F just fine. I believe the license for a wideband add-on saves you the hassle of setting up the conversions, which I've already done on this unit. I've even posted a thread with the settings for A/F and boost.

FWIW, there are numerous add-on licenses that can be purchased to add extra features, but this Dashdaq is fully functional and doesn't need any of them to datalog A/F, boost, etc.