As far as the difference between the ER18s and the Statements, In my own words here goes...
I think if you have a large enough room to place them correctly and you listen to a lot of rock n roll or heavy metal, build the Statements. If you have a smaller room and listen to more jazz or classical style music, build the ER18s. I heard a lot of guys say for longer listening sessions, the ER18s were easier to listen to. The room we did the comparison was less than ideal for the Statements. It was about 14' wide, and about 20' deep. I was told ideally you want at least 12' between the Statements, and 18" from the wall to side of the cabinets, which would be at least a 15' wide room. The listening chairs were set up about 10' (I think?) from the front of the speakers to the front row of chairs.
The Statements have better bass, you can feel it more. That's not to say at all that the ER18s don't have enough bass, but the Statements just have more. IMO, the ER18s play a more realistic reproduction of the music; I felt like I was listening to the music the way the artist intended it to be listened to. The ER18s are also definitely more efficient; the ER18s were almost as loud at 28 as the Statements were at 22 on the volume.
So far it sounds like I'm totally pro ER18s, but here's where the Statements really shine IMO- If you're like me, and you're more of a "check this out" kind of guy and tend to jam the volume as loud as you can get it w/out distortion when you show your buddies your new creation, the Statements will be louder and a bit more showy to the untrained ear.
I built the Statements for my dad, and built the ER18s for myself. I can't handle the girth of the Statements, to me they're just too big. The ER18s are large, but the Statements are huge! So the question is, aside from the sizes of them, am I happy I built the ER18s? To answer that, I am completely happy w/ them. While I do tend to lean more towards rock, I'm all over w/ the music I listen to so I think the ER18s are a good fit. I might find a sub to build to compliment them, but I'm not sure yet; I need to spend more time listening to them w/out a sub first (I haven't even heard them yet in the room they're going in, which tends to make speakers play a lot boomier). I would like to someday hear the ER18s next to the mini Statements. I think that may be a fairer comparison for both size and price (after all the full size Statements are bigger and about $200 more to build). The only downside is that the floor where I'm putting the ER18s is tile, and that brightens the highs up a lot. I'm going rug shopping soon!