I love this! I did a lot of origami as a kid, and I've been dissatisfied with my current seed envelope options—most recently I've been using #3 coin envelopes, but I don't like that they cost a non-negligible amount, nor that the only options for sealing are insecurely, or one-time use.
I went on a little YouTube bender and tried a number of different patterns along these lines. I did cut off the extra paper to make a perfect square to have a fair comparison on all of them—not sure if they will all work while leaving the extra paper attached as in the original video. Here are the versions I tried, ranked in my opinion from best to worst:
The original poster's version. I borrowed an image from this other thread discussing the same technique
that I think makes a nice supplement to the video. This version is my overall winner. It's the easiest to fold, holds a lot, and closes well. The image suggests an option to add a couple staples that would improve sealing security (though I believe it is misleading about which layers to staple). The only downsides are that it's not rectangular, so if you're organizing in a box it might fit awkwardly, and the security of the seal is okay but not great—if you jostled this around it could potentially catch and open.
The video uses smaller squares of paper, which is fiddly and produces a comically small envelope—great if that's what you need but too small for most uses. But you can use the exact same technique with a full-sized square and get a very nice size envelope out of it. It's very close to the same technique as #1 but with a slight variation that changes the dimensions. I like that this version is rectangular, and I find the security of the seal to be a little bit better. The downside is that one of the steps (folding the first top flap inside) becomes a bit trickier. It's not too bad with the full-sized sheet, but it could be enough to stymie someone without papercrafting experience. And with the smaller size paper it's downright frustrating.
This version is pretty easy to fold, creates a nice narrow rectangular envelope, and seals securely. The video uses a printed template, but there's no need, you can fold with scratch paper and just eyeball the dimensions like all the other versions. Downside: having a fold in the middle of the seed pouch limits the capacity it can comfortably hold—if you fill a nice plump seed packet it isn't going to fold and seal cleanly any more. The result is a higher ratio of folded paper to effective inner volume, which is probably not a huge deal but bumps it down a little for me.
My least favorite. Video shows a quarter sheet that again comes out very small, but can be made with a full rectangle of printer paper. Suggests a printed template but can be made without. This version is the clear winner for secure sealing if you get the little paper tabs in right, though frankly if you need this much seal security you should maybe just consider judicious use of Scotch tape or ponying up for commercial envelopes instead. Downsides: This is the most complicated fold of any of the versions. It's not rectangular, and in fact to sit flat on end, it has to be set "upside-down". Unsealing and resealing is a huge pain as you need to entirely unfold it and the creases interfere with access. Needing to re-fold the sides to seal after filling opens you up to seeds sneaking out of the main compartment into creases and folds, to later be lost or spilled all over.