Opodo is completely safe, I used them to buy J tickets twice (1x long haul and 1 x short haul), and there's not been much to complain about. Customer Service was also quick to reply, polite and efficient on the phone as I had to call them once. They also do the check in for you automatically as soon as it's up and send you the BPs.

Only thing I would warn you against is their practice to charge you a ridiculous sum to select your seat. If you actually get the app from the carrier (not sure it works with all, but it did with LX) you can actually select your seats for free as soon as you log in your reservation number, so that was like $100 thrown out the window. (I didn't want to be sat separately from my family as it happened to us with LastMinute.com whom I'm sure did on purpose).

I still recommend Opo over LM any minute. Just say no thanks to seat reservations.