There is such a lot of diving activity around here that many, many operators get positive reviews. But when a DM course offers what appears to be a fantastic opportunity, what is left unsaid or left to the prospective DMT's wishful thinking can easily lead to unrealistic expectations. I don't believe our operators try to willfully mislead; they simply leave some things open to the customer's romantic imagination. As long as your expectations and understanding of what you are getting are realistic, you will be in a better position to evaluate the advantages of each program you consider. So please keep an open mind as you read (don't get defensive) and let me see if I can explain a little more fully.
DMing on a liveaboard is hard work with long hours, and while DMing on a speedboat trip means you work shorter hours, there's a lot more lifting and carrying and switching out tanks involved because there are no compressors or quick fills on speedboats. So both are rather tiring, actually exhausting after several days in a row of it. Being in the water DMing is a very different experience from being in the water fun diving, even if a manta does pass overhead and you get a chance to gaze in awe. I go to the Similans regularly as a working instructor, and of course it's always nice to dive up there, but when I really want to have a good time and do my own diving, take as many pictures as I like, relax between dives, etc., I take advantage of discounts, pay for a trip and let somebody else do all the work. As a matter of fact, this is also true of diving at our daytrip sites, which I've dived hundreds of times; if I want to simply enjoy the dive, I pay for the pleasure.
Why pay when I already go for "free" all the time? When you are DMing, it's not your dive; it's the customers' dive. Yes, you are in the water, but your enjoyment is entirely secondary. As a DMT unfamiliar with the dive sites, you will not be leading many dives, if any, (as a customer, would you be happy to pay for a dive trip in which your dives were led by somebody who didn't know the dive site well?), so if somebody has to surface after 20 minutes with the air hog and misses the manta sighting, for example, that will be you!
Why become a DM? That depends entirely on the candidate. For foreigners who want to work in this region, most often the DM rating is a stepping stone to the Instructor rating. For those who want to work in their home countries, it may be the case that they simply like to lead dives and don't have the patience or inclination to be teachers. I just finished with one DM student who had bought a small diving speedboat in the Caribbean for her own pleasure, not as a commercial enterprise; she believes that divers on her boat are her responsibility, and she wanted to gain the knowledge and skills to be a competent dive leader when she takes people out diving.
Are you from Austria? Ukraine? If so and you are hoping to work in the diving industry, I don't suppose you'll be doing much DMing in your home country, but it's something to think about. What is your objective in wanting to become a DM? Where do you want to work? In fact, in many places like Thailand, getting a work permit as an Instructor is imperative for foreigners because local citizens are preferred as dive leaders (and in many cases aren't really even formally trained as DMs anyway). Also, in many places instructors spend more time DMing than actually teaching scuba, but they are more versatile employees since a DM cannot teach, but an instructor can DM.
Does all of that offer any insight in regard to your questions? Does it raise further questions?