do you guys think that such types of sleeves suffice for the air to go in the bag or do you need possibly an extra protection in terms of plastic case or something, esp. for long travels on the plain where you might lug it around with other baggage and put it on top shelves in airplanes?
I think a sleeve in a decent bag is perfect for travel. Frankly a decent bag is enough. The computer can withstand a bit no doubt, the SSD even more due to the lack of moving parts.
These people with just a sleeve seem to do ok. For me a bag is necessary as I don't want to just carry the thing like a book and I want to be able to store a magsafe when I travel.