Before you dock your Sansa, you need to attach to the speakers a model-specific spacer (two are provided) that keep the player sturdy. Though we recommend using them, they can be a pain when you're mobile, as it's an extra piece you need to account for. I also don't like how the dock too easily pops open with some pressure on the backside.
The power button on top glows blue when the unit's on, matching the Sansa's blue scroll wheel; while the rubbery plus and minus buttons control master volume. I'm not really into this type of feedback-less button, but there is another way to control volume. Though the Sansa's audio is fed to the speakers via the dock connector, it's not line-level. Because of this, you should be wary of your player's volume before docking. On a positive note, you can control your volume using the player's wheel (in the e200's case), just make sure your player and speaker volume levels are optimized. Back to the dark side: When you turn the unit off, then on again, volume jumps up to a high default level--not good with a baby in the house. Also, I wish the iM510s had a remote control.
The iM510 speakers will charge the Sansa player while docked (even with speaker power off), and the pass-through mini USB port allows for syncing--even without the Sansa's proprietary USB cable. Additionally, the subwoofer-out jack opens up the possibility of adding subbass to the mix (specifically, a model BB2001 subwoofer). Though the AC adapter is wall-wart style, we would have appreciated a case-friendly flip-out-style plug. Sadly, the iM510s are not appropriate for viewing video on the Sansa e200, since video plays in landscape mode--you'd be watching sideways.
The iM510s' most redeeming quality is their balanced and crisp sound. The four drivers deliver punchy sound with reasonable amounts of bass for a speaker system this small. They are powerful enough to fill a small room, and with batteries installed, they can add amplified sound to your travels (up to 24 hours of battery life on four AAs). Again, remember to keep volume levels between player and speaker in balance, or you'll get distorted or crackly sound at high volumes.