A good, loud little headphone amp. I usually use it with a clean, unprocessed output setting, plugged straight into the output of a effects pedal. I have also used it as a pre-amp to drive another amplifier (when it expects line-level instead of instrument-level signals).
The amp models are each combined with a given effect, like tremolo, chorus, or most frequently, reverb. That effect can be adjusted or turned off. Some models have overdrive built-in, which does respond to dynamics. It could maybe replace a simple pedalboard in a pinch.
I have plugged the USB-C output interface to my computer and directly recorded without any problems. I have also connected it to my phone without problem.
The Bluetooth input allows me to connect my phone to play along a metronome, or YouTube videos. This makes the setup much more manageable than a wired Aux input.
The battery is good for 3-4 hours of continuous use, which isn't much, and will give you no warning before shutting off. But it charges quickly via USB-C, and you can use it while charging.
The input of the amp has little capacitance and a high impedance, so when plugged directly into a passive bass guitar, it will give a maximally bright tone, which is pleasant but not usual. The built in EQ range is too high to affect the tone of a bass guitar significantly, so I leave it turned all the way up.
You may want to update the firmware via a special Windows program, available from the Fender site. This is a bother, but I've only had to do it once so far.
Finally, a feature not mentioned is it seems to have some kind of noise gate built-in. Once a note is muted, you can hear the background hiss rapidly drop in volume until the next note is hit. This is a very pleasant feature that makes this amp feel much better than other pocket headphone amps.