Has anyone used that travelling shop?

Its a one time use item too. You get 5 in one set and after using it 5 times you need to buy a new set.

Just as a side-note, unless you REALLY need to NPC stuff I don't really see the traveling merchant beneficial for a 4th job mage. The pots inside are normal pots (read: standard 1+:1 HP pots and 2:1 MP pots. Really bad because of NLC pots. You can recharge all stars except Furies I'm sure, since they are NLC exclusive. A funny note is that you CAN possibly attack and open the merchant. A BM in MSEA did a trick where she was able to continue attacking Grandpa Boss with Hurricane while she opened up the merchant in order to buy more MP pots.

Hurricane and Rapid Fire (corsairs skill) work differently than all the other attacks. If you click outside maple window or bring up any error message (trying to drop something while in breathing state, etc) it will continue to spam Hurricane or Rapid Fire until your mp runs out. Assuming you don't get hit by the monster in middle of it too, if you do then you are done for since pet won't repot hp.

You might still be able to open the shop and attack normally, im not too sure because the family window is like that too. I was able to continue casting Blizzard while family window was up. If it is like that, you can drag it into a corner then keep using it until your training session is done