1x800 gives you 66 seals and 5 guaranteed hashi frags, on top of that you get hashi frag every 60 pulls, so 13x 1-2frags and 20seals towards next hashi frag. So anything between 18-31 frags. If we asume 1 and 2 frags have same drop ratio, your average hashi frag gain is 19,5+5=24.5. Required starting seal ammount to start pulling (you need to get this much on your own): 734.

1x500 gives you 66 and 2 frags. +8x 1-2frag. Total of 10-18frags, 14 on average. Required ammount to start pulling: 434.

To sum it up:

-you need to get 1168 seals on your own in order to do both rebates

-you get 7 guaranteed frags from rebates and 26-52 frags from pulls. Anything between 33-59. With average drop rate thats 7+39=46frags.

Given how you said that, i asume you need 46 frags to recruit him.

6x300 gives you 6*66=396 seals from rebate. During that time you get 30x 1-2 frag, so total 30-60, so 45 on average. Required starting seal ammount to start pulling: 6x 264, total seals you need to get on your own: 1404.

Looking at hashi frags as the only factor, hashi rebate is faster. BUT looking at second option where you need to invest 1404-1168=234 seals more, you get to draw 1800 times instead of just 1300. Duing those 500 draws you can get a lot of materials, duplicate ninjas=more frags (slightly more power from ninja scroll feature) or super rares from edo jinchuuriki treasure if you decide to pull there. You gain a lot more here, as long as you dont have all the other edo jinch already.