It's just a carb powder
. When you exercise, you burn off fat and some of the carbs (glycogen) stored in your muscle fibers. So it's usually a good idea to replenish those burned carbs, because that's what adds to your muscularity.
So after a workout, you should consume a protein shake with a decent amount of carbs and some simple sugars. But nothing excessive, if you're trying to stay lean.
That's why I use Glyco Maize. It lets me control the amount of carbs I consume. If I had a really hard workout, I can add two scoops instead of one. With weight gainers, it's a set amount of carbs and proteins with every scoop.
Plus, most of the weight gainers I've tried in the past gives me gas and stomach bloating. Which is the reason why I'd rather mix an MRP shake or just plain whey protein, with the carb powder.
Honestly, I think you should avoid weight gainers. You're pretty lean right now. And I don't think your workouts are at the intensity level where you need to consume massive calories. If you consume more calories than you burn, then you'll just end up getting pudgy.
It's all up to you. Everyone's body/metabolism is different. So weight gainers might work for you. Or it may not. You can try it for a few months and see if you're satisfied with the results.