I prefer the ease of use of the "peel and stick" sealed envelopes and use varied sizes of them. I have found them all to be of good quality and a value for the money - not "flimsy" and capable of holding a useful quantity.
I use this product to send packets (business proposals) out to agencies. I prefer the white envelopes to the yellow because they look crisper cleaner or more professional.
I use for sales calls on the road. I carry the envelopes and when I come across prospects or customers who work from their house instead of a business location I put info in and mail at nearest post office.