This may be an unpopular opinion, I don't know, but I'd hold off on submitting to Seedpod until the little fic has been rejected everywhere else. Nanoism is a good start, because they have the lowest acceptance rate of all the Twitter fic places I've looked at, something like 15%. Trapeze takes about 60% and I haven't looked at Cuento or the others specifically for acceptances, but I think it's pretty high, too.
Seedpod, on the other hand, has a 100% acceptance rate at Duotrope. I'd send them a Twitter fic if it got turned down everywhere else, and may yet have to do that with the one that's been at Nanoism for 50 days. I'd do it, just to get it read by someone else, absolutely.
But I'd never start there, because it's not something you want to put in a cover letter, not when they take everything. There are several places I've published that I wouldn't list in a cover letter with a submission, because I know it's just not going to help me, and may make me look a bit naive. A place that takes 100% of submissions is like listing something you put in your own blog as a publication. Technically, it is, but it doesn't show that someone else read your work and chose it over other work, which is what makes an editor pay a little closer attention to your submission.
I hope I make sense, and don't sound like I'm knocking Seedpod or anyone who's sent stuff there. I'm not. I just think when you look at the grand scheme of things, it's best to start with the harder publications and save the takes-everything ones for the last resorts. It pays to think in terms of 'how will this benefit me the most?' like you might with a career.
Shelley