Personally I'd recommend looking at Labuan Bajo, which is the gateway to Komodo National Park, lots of day boat diving as well as some liveaboards
I know Blue Marlin which seems to take the DM training seriously, and the DM trainees I met were pretty good.
As instructor, who teaches DM courses my advice is the following.
Get your basic skills up to scratch before hand, by that I mean shallow water buoyancy and trim. You'll be spending lots of time in the pool, and this stuff needed to be automatic and instinctive - if you're buoyancy if poor your skills tests will be difficult. When assisting students you need to be focused on them not sculling about to stay in position
Refresh before hand all the basic skills - there's plenty of videos. The course can then polish them to demo standard
Make sure in advance you can complete the swim tests inside the times. The details of DM training is contained within the crewpack training manual
In advance get your dive theory up to scratch before hand, again lots of online resources.
The more prepared you are, then the more you will learn and more time can be spent on teaching you new skills rather than lots of remedial teaching to get you up to scratch.
Everyone will have strengths and weaknesses, as it's a mentoring course students are expected and encouraged to help each other with skills and theory practice
In Komodo you'll get great experience in a fab location and some great social life between the dive centres.
With DM training, the more you put in the more you get out, it should challenge the student the ensure they get value, equally the Students need to be honest with their experience and ability so we know before hand, after all the truth will become apparent.
It can be a great course, obviously research your dive centre to make sure it fits with all your needs