Solid rail system. Very sturdy. But I will warn you. The Echo 1 E90's upper rail doesn't have quite big enough cavities for those two blocks to fit into. You will have to do a lot of sanding/filing of the blocks to get them to fit. Do your best to get them to fit completely flush within the cavities, though, as that will prevent your rails from being crooked. As with the three screws, just don't tighten one all the way down before you thread the other ones. If one's not lining up, undo the screws and start with that one. Trail and error.
Otherwise, this rail system is very convenient to have. It makes your P90 feel more like a special forces rifle, especially after you put on attachments. Putting a foregrip on here makes the gun very comfortable as well. The top rail does not line up with the upper rails on the P90, for those of you who wouldn't know.
I give this a 5/5 because once its on there, its there. Its easy to take back off, and when those blocks are stuck in there, you won't have to worry about losing those. There's no worry off it being loose or not being able to support the gun's weight. This is a VERY solid RIS.
Solid full metal design
Not a whole lot to the installation process
Doesn't add too much weight to the front
Can support the entire gun's weight
A Madbull XM203S launcher does fit on the bottom without looking completely ridiculous
ECHO1USA.COM on the side may be cheesy
May or may not be overpriced when compared to the KS rails
Takes some time to install into an Echo1 E90