Ark has the same "back up your proof every vtxo" requirement. And the same limitation: the moment you receive offchain vtxo(and proof), you can unilaterally exit, but it isn't exclusive either — a colluding previous owner + ASP could still double-spend your prior state. What's better about Ark is the periodic batch round (an onchain tx). When you participate, your old VTXO gets forfeited, which kills the stale state a prior owner could've exited with — so exclusivity is restored and only you, the latest owner, hold full ownership. And the batch settlement is O(1) onchain regardless of participant count — thousands of participants still settle into a single shared Taproot output that just looks like a normal address. (You only unroll the tree if you unilaterally exit.) That amortizes the fee across everyone, so at scale the per-user burden becomes almost negligible.