Pure f2p player here, never done a 1st recharge ever (though I get tempted to every so often, but ever since I got my Gaara to 3* with events and Black market, that temptation is now gone).

I use to buy magatamas, but regretting it now. Few months on, now I just save and use it mainly in Lucky Dice only. Most * for buck to bring the most out of the hard saved coupons. Do it right, and for my situation, I'm actually on the way to getting my Cursed Hidan in a month's time!

And if you're not aiming for any ninjas in particular, then spend coupons on power items during events. Don't really recommend saving for Ninjas though, especially if you have a team that you have drawn from Kage treasure.