NOOOOOOO!!!!!!!
Use adequate protection - practice safe sax.....
If you really must use a gig bag, then the Tom and Will one's are quite well padded and good value for money.
No gig bag will ever protect your instrument against damage. A Tesco carrier bag would be just as good.
I don't recommend using a gig bag, although I use one myself. Someday I'll regret it.
Lightweight cases like this offer better protection -
http://www.sax.co.uk/acatalog/Gator_Cases.html and obviously most sane people would use a Hiscox hard case or something similar
If you do go mad and decide to use a gig bag, then be prepared to keep a careful eye on your instrument at all times - be aware of all possible things you might bang it against - door frames etc, at gigs stash it somewhere safe (eg behind the PA) away from people loading stuff onto the stage, keep it on your knee on buses, always check it's properly zipped up, make sure the strap is secure..
in general, be ultra careful and paranoid about your precious horn in it's non protective container....
You're far better off with a hard case and the only excuse I have for not using one is that I don't have a car and thus hurrying across town to the bus stop/train station etc is a lot easier with less weight on my back and it attracts less attention from muggers, junkies, and drunkards wanting you to play 'Baker Street'
Since I'm trying to get some gigs abroad, I'm saving up for a Jakob Winter alto hard case - the 'Eastman' fibreglass one is fairly light (1.9 kg) and no more expensive than some of the pricier gig bags, or I might go mad and get the even lighter Carbon Fibre model (1.3 kg) which is still cheaper than the cost of getting my horn repaired