Saving enough seal scrolls to get more of his frags from 500-1000 seal rebates. will still take about a year or so to get him this way.

GNW better cuz u will get more and better ninjas to use.

In my personal experience I think its better to use 300 together each reabate ( not the one that gives 7 days seals ) gives more frags than 500 or more

I spent 600 got 15 frags but when I spent 300 I got 11 that's why I kept using 300 only to get 10-11 which made me have 57 frags now with 1800 seals

every 40 rolls you do in gnw or time limited treasure grant you 1 fragment in average (is actually a chance to be 1 or 2, with 50-50 chances, every 60 rolls).

lets consider the 800 rebate vs doing in 3 months twice the 300 and once the 200 rebate.

the first 300 grant you the same outcome, so the comparison is between the 5 frags you get by hitting 800 and the 66+36 additional seal scrolls the rebates the following two months will grant you.

102 seal scrolls are, in average, 2.5 frags.

so, by doing the 800 rebate you actually get 2.5 more fragments in average.