I took a quick look at the site and got the impression that it was OK. The explanations are generally good, but some example sentences have mistakes. Also, it seems to be a patchwork of various things without much organization. Here's some example sentences from the site: | 아플 세라 약을 먹기로 하였다 | = In fear that it would hurt, I decided to take the medicine. ** Not the best translation. | 난 행여 그녀가죽을 세라 두렵다 ** somewhat uncommon usage example. Bad spacing. | = I’m afraid that she might possibly die. But those are probably a minor thing. I think the best way is to look at diverse sites for a period and decide, rather than trying to screen them in the beginning. 고마워! is an improper way of saying "thank you" in this case. When you're addressing an indeterminate multitude, as on a social site, you should always use a polite form. It should be either 고맙습니다 or 고마워요 (or 감사합니다 and 감사해요).

i think Russian letters are more suitable for a western way to write Korean sounds