Hey,
I've got the 879 RR, and I can tell you,
I got it cheap and I think I did the right thing. The sound is good but nothing compared to my other boxes. You can turn it up to maximum volume and it's still not THAT loud. It's light, almost too light... Basically it looks great, works great but is a big black empty box. I bring mine if I have to go somewhere risky or if there are rain clouds.
Probably the 878 has similar qualities.
I'd go for it though, it looks delicious

.
Peace