I would say it's not as profitable as drawing from life... but it does have some advantages . . . it's a good way to really STUDY something visually, which is a component of drawing--learning to really observe--it's good for this for one obvious reason . . . it's NOT changing! Because of that, it is also an excellent way to study rendering. (The depiction of how light falls on an object.)
When I was just getting going with all this art stuff, I had a more experienced artist recommend to me the following proportions for drawing practice: 1/3 from life, 1/3 from photographs, and 1/3 from your imagination. Now that I'm more advanced, I'd say, "okay, this is a little oversimplified" but in principle, I do agree with the point he was trying to make. Each method works a different artistic muscle, they're all profitable. But just because eating blueberries is good for you, it doesn't mean you go on an all blueberry diet. Mix it up, it's more educational.
Even though it's a little more, I would go with the regular box.
Here's the deal. The "Cotman" line is Winsor & Newton's "student grade" paints. My advice to you: NEVER, EVER buy student grade! The thing with student grade art supplies is there is ALWAYS a reason why they're cheaper. They will just make your life more difficult in some way, so it isn't worth it.
In the case of student grade paint . . . the paints may "look" the same--if you wet both and paint a swatch, you won't be able to tell a difference, but as soon as you mix a color, say mixing green using blue and yellow student grade paints...if you do the same thing with the professional grade, you'll see a HUGE difference in the quality of the mix.
So . . . stick with the more expensive one would be my recommendation.