Bullshit and it sounds like you're not an ectomorph yourself. Because that is the fastest way to getting fucking fat not muscular. I'm 6'5 and I started out at 155lbs. 10 years later I was 250 at my biggest and most ripped. 50 of that 100lbs I gained was due to abbreviated training. It didn't matter what I ate if I overtrained I wouldn't grow. I had to cut down my training to 2 workouts every 8-10 days. And I still had to eat around 5k cals a day. But those weight gainers are shit and they will lead to an ectomoprh getting fat. The best thing an ecto can do is focuse on high fat high protein and moderate to low carbs. Once an ecto becomes a fat burning machine watch out they have some of the baddest physiques in the gym.
When I started training, I weighted all of 136 lbs (most of which was my high-top fade from the 80s), at 5'8" or 5'9". The simple fact is (whether you believe it or not, as if I care one way or the other), the weight gainers are what I used to get bigger and stronger. Staying that weight-gainers make ectomorphs fat is bordering on the absurd. Quite frankly, they're the ectomorph's best friend, as they help get them the quantity of calories they need to grow.
It took pushing 6000 calories a day, just to get me over 200 lbs. But, I'm really not an ectomorph.

As I've said earlier, the quality of gainers now are better than they were back then. And, they're more economical (especially, if you get them on clearance).