Pretty sure Spaten uses the regular 5l mini keg with the replaceable bung, not the single use ones like Heineken, right?
I actually forced carbed both beer and apfelwein in cornies and then filled those little steel kegs, simply raised the carbonation slightly to amount for any possible loss and filled like I might a growler. I took the extra precaution to keep them cool (especially the apfelwein as I backsweetened without pastreurizing) but I think both precautions of higher co2 volume and cold were ultimately unnecessary for the beer, even pouring from the bottom tap it had PLENTY of co2 on the first day (and one open keg still had a reasonable head on it the next evening, despite having the gray open vent bung on the top)
This is after more than a week and travelling 1100 miles in a cooler in the trunk.
If you're pouring from one of those countertop kegerators on co2, I'm very sure you'll be happy with the carb level if you have it filled like a growler. Just make sure to wash it first!
BTW, considering buying a countertop dispenser for a gift, would you recommend the one you have, and what is it?