The Mangroves venom has shown to be pretty toxic in some cases. How ever they have an ineffective delivery system. Every snakebite can cause serious problems if not taken care of properly. If your truly considering the Mangrove make sure you do your homework, Ensure that its legal where ever you are. Read up about the bites and husbandry of the snake. and most of all in my opinion you need to treat it like any other venomous snake, with the up most caution and respect as it could inflict serious damage, and use the proper handling tools and tactics.
Why not try something like the Sulawesi Rat snake, or some of the other old world rat snakes or some of the other python or boas. I'm not trying to steer you clear of the Mangrove snake, it is a beautiful snake, but at the same time I believe that people really underestimate it.
Brad