Not Netto, but we had a slightly different experience with a cheapo clarinet - Stagg.
It played, but was very crudely made. So crummy that when some bits got bent, the instrument builder refused to work on it - he spent a bit of time showing us the manufacturing faults, and showing us why it wasn't worth spending money on.
Still - it did the job, and cost us less than the rental would have on a decent clarinet for the year... And a lot less than the depreciation on a decent one as well, always a big factor when a kid's starting out and you don't know if it's going to work out or not. It's also still playable and acts as a (reluctant) stand in for when the decent one is in for repairs/service.
Something else to consider is that a lot of the teachers at the local music school use cheap instruments for gigging, saves the risk of damaging an expensive instument. One teacher blows a blue

lacquered flute... Sounds OK on it as well... But apparantly it's harder to play well than the recognised student flutes like Yamaha, Jupiter and so on.
So I guess it's a case of going in with your eyes open. If it doesn't play you can always take it back... And if it plays OK, it's a good starter/standby. A reasonable clarinet mouthpiece isn't going to break the bank if one's needed....
Hmmm - we have netto here, but I've never seen them sell instruments.