I have tried:
mouse and keyboard
tablet (no screen)
tablet (with 4K sceen)
remote desktop (using my iPad)
and done this with a variety of other programs.
There are a few pros and cons.
When I hear efficient and tablet, this is what I think said person means. if you can draw on your screen like paper, the feeling of efficiency comes from how you can directly control (sculpt) the character. That is fine and dandy, but not everyone's cup of tea. In fact there are a few issues if you only use the tablet.
so here are two things to consider: interactions, and actions.
An interaction would be like sculpting or texture painting, where you are just clicking and brushing along, were it is not a science.
An action would be like clicking a button or hotkey commands.
In terms of interactions, tablets are pretty good (but not perfect), they allow you to have direct influence over your work. But it is not for everyone and it has some issues. I myself am more of a mouse user, and I know (heard) of some artist who have amazing skills using a mouse. It is all a matter of control, if you have a small tablet, you have to focus on wrist-based actions, which only really allow for short controlled lines, not long lines. If you have a large tablet, like a sheet of paper size, you can use your shoulder muscles to have large smooth strokes. Using a mouse, however, you can have multiple sensitivity settings (I really recommend a high dpi gaming mouse, gaming mice such as those by Razor allow for on the fly dpi adjustment) so you can adapt the sensitivity if you want to. Mostly moving between shoulder action, wrist action, or finger-based control of the mouse and thus control over the work. two issues with tablets are their scene and their texture. The screen has to be high enough resolution that it is like drawing, you don't want to be looking at pixels. I also find that tablets get to warm for me, even with something on my wrist to protect it. another issue with screens is the distance between the surface and the screen. there is a small amount of glass between the pen and the screen. so it can really mess you up because it seems like your pen is always floating so it is hard to have good control. I find the iPad is the only device that truly solves this issue, not sure about the second generation iPad though. lastly is the texture. I like the texture of paper and pencil, it allows me to have good control. tablets with screens are often too smooth for me. I have heard of people finding good screen protectors that provide the texture they need but I avoid them because they further lift the pen away from the screen.
Now about actions. I would say, if there are buttons, the tablets win. if you can directly press the button, it is often quicker to do that than to move a mouse. hence more efficient. I game a lot so I actually have better mouse control than pen control so I am ok with the mouse but definitely can be strenuous.
However, if hotkeys are involved (blender is hotkey heavy) keyboard wins, hotkeys are much faster than anything, that is why some higher level programs (such as how blender was originally made by artists for a studio) focus on hotkeys. hotkeys are the most efficient.
Now you could get away with say, a tablet and a keyboard and try to get the best of both worlds. One issue I have is trying to understand the shape of a model, hard to do on a 2D screen, I really want to get the looking glass holographic display, but until then I have to simply move around my scene a lot. In order to move around however, you either have to click an icon on the tablet, or use a hotkey (mouse or keyboard) to navigate the world, if you need to move around a lot the tablet is not so good because of all the great motions you got to make and it will tire your shoulder out, but a mouse could tire your wrist out.
either is good and it just depends on what you want to get good with. I prefer keyboard and mouse mostly because I invest in better ergonomic stuff, which is not something you can do with a tablet, so I minimize working fatigue.
hope some of that gives you something to think about.
