In terms of visibility to ATC, my personal opinion is that a mode C transponder would be better than a Skyguard. I think that as of today, very few ATC facilities are processing ADSB-out signals and presenting any data from them to controllers. A Mode C transponder will at least respond to a radar ping and allow your return to get tagged with a datablock that includes your tail number and altitude on the controller's display.
Keep in mind also that the Skyguard device is not certified compliant with the 2020 ADSB-out mandate, and probably won't ever be, at least in its current form. I doubt any portable device will be. You will eventually need something certified with ADSB-out unless you want to be highly restricted (or illegal) in your flying.
The benefit to a device like Skyguard is weather and traffic in the cockpit. It's sort of an "early adopter" way for pilots to get the in-cockpit benefits of the ADSB system right now.
If budget is limited, there are ADSB-in receivers that give you all the ADSB weather benefits, but traffic is not complete since it will only work when someone near you with an ADSB-out device "wakes up" the transmitter and your device can hear the broadcast.