Seems like a blatant rip-off of Let's Encrypt to me. Just look at the last line: "Let’s start to encrypt now." Really? Besides that, it's also not open source at all, you have to install a daemon to manage certificates, and although they mention wildcard certificates "(5) Not just for one domain, but up to 120 domains with wildcard support," this is apparently part of their "Pro" plan. Who knows how much that costs -- why would they have a lite and a pro plan if one did not cost money? I feel like sticking with Let's Encrypt is the best option.
startcom is an old player and as far as I know they were the only one offering SSL for free for a year "class 1". Let's Encrypt is shaking the market.
As far as I have read, you get max 5 SSL certs fro free from StartEncrypt and you have to register for that first and get an account at startcom (unlike letsencrypt where you don't have to register) and you need the pro plan to get certs that with a higher trust level than letsencrypt. So I see only disadvantages compared to letsencrypt as long as you need just domain validated SSL certs.