I looked into Planesmart and I don't know how closely the business model matches Airshares, but Planesmart made NO sense at all.
Most are all doomed to failure, because they are not a simple aircraft rental operation, but a convuluted mess of shared ownership, professional aircraft management, club type operations, etc.
First problem I encountered was they had no planning beyond the first three years with a new aircraft that is under full warranty. So when the question was asked about who pays for a new engine at TBO, they looked at me with blank stares. So I'm thinking, great I have an aircraft that I may not even fly because of the aircraft pool model and now I have to pony up for 1/8th or 1/4 of an engine, BS.
Same question becomes ambiguous when you ask, "what happens if someone is flying the plane and burns up the cylinders?". They said, "who ever did that will have to pay for it". I said, "how do you prove who did it if 5 people flew it the week it happened?". Answer is no one will admit it, so once again the "owners" get a nice bill that month for their share of a top overhaul that they had no part in causing. Even simple things like flat spotted tires are likely to happen quite often and or course no one will know anything.
Last, the pool idea works if you have a lot of exactly the same aircraft. So if you "buy" a turbo, that doesn't mean that's what you fly since they may not be available when you want one, like on a holiday weekend.