Half barrel is working so far for me. I put ~13 gallons in there and it's chugging away.
Being able to boil/steam sanitize the kettle was nice. I experimented with oxyclean soaking my carboys for a while to make sure I'd be able to clean a keg without brushing. I don't think I'll have any trouble there.
Something I'll be getting soon is a small funnel. The kit has a small blowoff opening that would work great for pitching yeast into, or adding dry-hopps, but the opening is less than half an inch. I'm looking for a funnel that I can sanitize and use for post-fermentation additions. Just something to think about.
One thing to consider is weight, mostly-full kegs are HEAVY. Think about how you're going to get it into your fermentation chamber.
Like I said, I'm just doing my first ferment with this, but so far it's been great. You can't see the fermentation, which takes some of the fun out of brewing, but I'll trade that for bigger batches, less cleanup and forced-air transfers any day.