I don't know anything about Blue Manta but here are few tips (feel free to ignore ha ha ) for first-timers to Indo:
If you're prone to "the runs" like I am
(or maybe even if you're not), take 4 Pepto Bismols / day as a preventative. Some studies show about 30% of international travelers getting traveler's diarrhea. It's not due to bad water.
Travel a few days early to the region. Sometimes people have trouble with customs or getting their baggage, etc. We like to go diving locally in Bali before a big trip to get all out gear (and our heads) squared-away before we get on a boat we're paid lots of money for.
Bali can be a nice spot before or after your trip. Traffic is awful though.
Jet lag coming to Asia isn't NEARLY as bad as jet lag going East back to the US.
If you get on the boat and the dive guide isn't working out, talk to him. If that doesn't work, ask the trip leader for a change.
Make sure you're squared-away regarding seasickness before you go. My wife wears the scopolamine patch on all boats, I'm almost always good on any boat.
You WILL have currents. The issue is how strong and what types they are. Resident DMs should be pretty good at spotting the bad ones, but no one can predict the ocean. Be sure to bring all your safety gear and know how to use it. If you're not used to currents, go somewhere like Cozumel to get some experience, it will help you be more relaxed. Being able to shoot an SMB from depth and to deal with a blue water ascent could be very useful. Your profile says 500 - 999 dives, so probably not a problem but there are a lot of currents here.
I hope this is useful. Feel free to ignore me, no worries!
- Bill