Terrain control works far better than some may have been led to believe, The documentation is fairly poor as already mentioned here, But everything that tekkit has can in fact be rendered in, if you know how, the documentation on how to achieve this is freely available on the TC forum.
unfortunately there are some severe lighting issues when using Terrain control to render a world, under certain circumstances, and too many b02's can make your render process very slow, and taxxing on the server and with b02's being at a minimum of 1-100 you'd be surprised how common 1 rarity can get.
If you don't have a pretty good server or pc to handle the render process, the map by image feature is probably the best choice for you, not to mention randomgen is extremely hard to control, even if you're highly experienced in terrain control, values of 0.01 can make a very big differience, or even glitch out.