Sites like these really just get you subscribers in name only. Sure, there might be instances where you get more views (as you described), but for the most part, what you get are inactive subscribers or bots that watch the video just to give you views. It's hardly a valid method; if numbers matter to you, sure, go ahead, but as has been said earlier in this post, subscribers does not equal quality, and while it might be a longer and more tedious road, it's much more rewarding to get your subscribers the old fashioned way; by producing quality content that people want to watch.