Yes, fees to exit unilaterally should be comparable to Ark as it also uses this kind of transaction chain to be broadcasted. There are many variables which can be tweaked: - number and sie of the leaves/vTXOs - depth of the chain to broadcast - timelocks - fee/rate Ark solutions have this periodical onlineness requirement and ongoing fees for rounds as wrll which make them have different tradeoffs. Spark works now, but no wallet should be locked in to it. Let it and the alternatives evolve. Our job is to keep our eyes open and assess the risks.