I'm no expert but I have a Sportco barreled .22 rimfire Martini cadet. my local gunsmith fitted a lovely scope mount and its super accurate and has accounted for many rabbits, hares and pigeons I have a friend who i would call an expert on all things Martini. he is in the process of building a 12 Bore rifle on a large Martini frame. and has built various calibers over the years on cadet actions and the full size actions. he agrees with me that its very difficult, if not impossible to find a Sportco barrelled cadet that is not accurate. so my advice, If you see Sportco martini at a good price, , just buy it and have fun.
I've had a couple of the 297/230 original cadets and I know that they are collectable and can be reloaded if you can find cases, dies etc, but for me its too much hassle unless you have really been bitten by the collector bug. There are a few guys in my club shoot cadet .310's in our Rook Rifle comp. they are easy to reload, cases dies and moulds are readily available and they're pretty accurate. not the prettiest action but you do learn to love them.