not worth seals, go for Ay , Minato

No clue when he will get his skill books or skill broken here but he is still a very viable character late game and used in place of kyubbi naruto ( in china). Also again not sure if it will happen here but he became one of the super rares for china's tendo treasure.

Sage Naruto it worth it even in future because of skillbreak .

Get him, hes a really solid ninja. Preferable way should be via events, not via seals.

In my opinion, Sage Nardo is NOT worth spending seals on just 'cause of the high chance of getting Ao or Traitoro.

However, he IS an extremely solid character (one of the few who can simultaneously play the role of a Tank and a Damage Dealer on a team) and you should shoot for him in events. In the past he's been pretty decently easy to get in the past, so you can probably amass fragments of him from there.

Sage naruto is worth to be used but there's no reason to spend scrolls for him since is almost sure that within 1 year of free draws in sage treasure you get him.

Spend seal scrolls he is worth

The thing we have to think about here is the overall * for buck when it comes to spending seal scrolls. Spending on Sage is like a really high risk high reward type of thing in that if you don't get him you practically just wasted your scrolls. I don't like that type of thing so I wouldn't rec it, but it's all about preference here.

If you spend in something like either Jinchuriki or 5 Kage, you at least have a chance to get solid characters like Mabui, GNW Tenten, et cetera from the commons. In Sage, all your commons are easier-to-obtain characters like Jugo...

Don't forget, that you can get a rare from sage that's a common in kage aka Ao.

i got my sage naruto out of free draws, after 4 months i was level 60. If you are lucky like i was there's no reason for you to spend scrolls. Anyways, if you ONLY use free draws, is almost sure you don't get dupes, so you get all the 3, as Zelgadis said, within 1 year (just to confirm that, i can tell you I got Ao last week, after 8 months of free draws).