The Hue Play Gradient tubes are Zigbee only and pretty much require the Hue Bridge to be interesting.
Unlike some other Philips Hue lights, they do not have Bluetooth for direct control from a smartphone.
This means you may be able to connect them to another brand's Zigbee bridge if you already have one, but it will probably appear as a single light with uniform brightness and color instead of individual segments.
The gradient effect is a Philips Hue extension and will likely only work through the Hue Bridge, so using them without the Hue Bridge defeats the purpose.
I didn't test if it can be controlled directly from a Zigbee switch, but again, I don't see the point as it defeats the purpose of the gradient.

The Hue Bridge acts as the controller between your LAN and Zigbee, and will let you control the tube from your smartphone, from the Internet, as well as synchronize colors with your music or videos (Hue Entertainment) if you install the PC/Mac Hue Sync app or buy a Hue Play HDMI Sync Box (both of which only send commands to the bridge, you still need the Bridge as the central controller).