Seafrogs SF-01 Strobe: buy or not?

I currently own (and use) a Seafrogs SF-01. Most of the time I am happy with just one flash, but due to GAS I should have two flashes. This flash works really well, no missed shots, reliable power. It uses two 18650B batteries, has double O-rings in the battery compartement, but not TTL. It is quite affordable https://www.unterwasserkamera.at/shop/catalog/de/product_info.php?info=p7724_seafrogs-sf-01-lz32-unterwasserblitz.html

A litte while ago I remember having read bad reviews but mostly from people who never used it. I understand that in case of failure or damage there will be little to no possibility to get spare parts.

Should I go for a second one or go for the better known INON/Sea&Sea/WeeFine/Retra...?

If you're happy with the performance of your one strobe, I don't see why not get the second of the same type. I used to shoot with SeaFrogs' earlier strobes, ST-100 Pro, and wasn't particularly happy with them because they were TTL-only with no way to adjust the output, but it sounds like SF-01 has a proper manual mode, so that is not an issue.Just make sure you get yours through a reputable dealer so that you have someone to talk to in case you need warranty support.