Do you think a balloon would break if you used it like a condom. It would be weird if it actually worked better than a condom lulz. Gotta give some nasty rug burns though.
At the risk of taking long-dead trollbait, it does seem that Japanese condoms do have the reservoir tip, as it's a punchline in a recent kodomo_no_jikan chapter.
Shiro, the older female teacher, is looking at a condom, sees the oddly-shaped tip, and freaks out, thinking that 1) penises have a pointy spike on the end and 2) cervical penetration by this spike is required for fertilization.
Looks like we're almost done for the seventh time. As I thought, doing it twelve times is pretty hard, huh? But I'm sure you can do it! Do your best, okay?
In Training with Hinako, exercises are done in sets of 12 or 24.Eh? Suddenly, it's all slippery inside me... What... It couldn't be, the condom...? I see, I'm prepared too! So, for the last five, pound me properly, ok?