Some very significant issues with CAMO.
First of all, it costs a LOT of money to have a CAMO. Count £2000 and more per year, at least here. They ask a basic fee for just having you, then a fee for every work order, then other stuff on top. I have decided for myself that if I am ever forced to enter a CAMO agreement that would be it for me as it will up the price per flying hour dramatically.
Secondly, you loose the right of say what to do and what not. You loose the "on condition" variant for engine and prop, as no CAMO will take responsibility for running an engine or prop over TBO.
Thirdly, the moment you have a technical problem outside your homebase, your CAMO has to take care of everything. You don't even have the right anymore to find a local mechanic to do simple work, EVERYTHING has to go through the CAMO, who in turn must open a work order (£££), if need be fly down a mechanic (even more £££££) and it is him who will decide as he is responsible.