I play nylon, steel and electrics with piezo saddles and I had high hopes for the AD-8. However, I was greatly disappointed when I tried it. The body didn't add anything usable (unless you like muddy low midrange resonance), the "string enhance" basically adds presence - the last thing you need with quacky piezo. The reverbs were lacklustre. The EQ is OK (at least it's parametric, but I find the EQs on the Baggs DIs are far more powerful and usable), and it can't be phantom powered - which I find essential with active DIs. Also strangely enough, it doesn't have the chorus or anti-feedback found on the lower AD-series pedals.
I ended up buying the Fishman Aura spectrum DI which while it doesn't have any effects aside from a very transparent compressor, actually adds a lot of realism - convincing enough for solo guitar. In a pinch, I'll use a Baggs Paracoustic DI. If I were on a tight budget, I'd probably look at the Zoom A3 or look around for an old Yamaha AG Stomp.