To reinforce the seal, you can put a bead of silicone all around the seam where the front clear lens mates to the back housing. The blacked out inside housing won't effect the illumination since the reflector itself is still chrome.
As for quality of the optics, that depends on how well they copied the reflector of the original. If the copy is exactly the same and was assembled into the housing correctly, then the light output should be as good as the original. Also the correct reflector will help focus your light to the light pattern onto the road. This is why trying to put HID in halogen housing will produce all kinds of glare and poor pattern on the road.
My concern with these lights is the material they use on the clear lens, as the OEM one is very robust and can withstand all the environmental abuse year after year. Not sure if these aftermarket lens would haze, or crack, etc. I am surprised they actually made these headlights for the Odyssey because it cost a lot of money to tool the die for the mold, and they usually will not invest that kind of money unless they are sure they will sell a large quantity of these lights. This is why cars like Civic and Accord have so much aftermarket parts available.
Another thing to note is technically these are illegal. The main reason is it's missing the yellow reflector on the side. The law requires that when you look at the side of any vehicle, there must be an amber reflector on the front and a red reflector on the back. Again this is viewing directly from the side of the vehicle. Now I said 'reflector' and does not matter if you have yellow bulbs inside.
Of course the law haven't stopped people from clearing out all the lights on their cars. I have been guilty of this in my younger days

D