Disadvantage of flashing to SHV-E210L firmware

I've got an SHV-E210L (Korean Galaxy S III) running on an I9300 firmware (don't know how).

I saw on SamMobile that an Android 4.3 firmware is available for the SHV-E210L. I wanted to ask if I'll run into any problems if I flash that firmware?

Will my phone get locked if I flash that firmware?
BTW, just telling you I don't mind the 80-character SMS limit or the fact that I can't use EDGE. Are there any other disadvantages of flashing a Korean firmware?

I've also heard of I9300 users losing their IMEI's after flashing to 4.3 and having excessive battery drain and random reboots. Will I get those?

Thanks

Sent from my GT-I9300 using Tapatalk