The D100 offers two easy ways to get the party started using either a Bluetooth connection from any compatible A2DP device or through the hard-wired 3.5mm connection on the back. We tested the Bluetooth setup with an HTC Evo and an Apple iPhone, and establishing a connection was as easy as holding down the power button for a few seconds to engage "discovery mode," and then just selecting the speaker on the corresponding music player. The entire process took us less than a minute on both phones from start to finish, and we couldn't ask for an easier way to connect.
The Logitech Z515 may have an advantage over the D100 in that Logitech provides a wireless 2.4GHz USB transmitter in addition to the aforementioned connection options so you can still get wireless music from your laptop without sucking up precious battery life on your phone.
On the other hand, we prefer the D100's range of sound over the Z515's across all of the test music we played through it; bass-heavy tracks are well-accommodated, and highs come out crisp without sounding tinny, an impressive feat especially for a Bluetooth speaker. The speaker can actually get quite loud at maximum levels as well, although don't expect the volume to blast high enough to get a large house party started. Bluetooth speakers like the D100 or even the Z515 are better suited for small get-togethers, not ragers.