Its a bit dated by flash standards of today but if it does what you need £50 aint so bad.
It wont be as powerful as the Sigma 500 you already have
specs available
HERE
Below shows how the different speedlite models work with the 350D
External Speedlite
Compatability: fully compatible with EX-series Speedlites; EZ-series Speedlites only operate in manual and stroboscopic modes; flash guns with external metering system (including the Speedlite 480EG) will synchronise at speeds up to 1/200 second; a synchonisation speed of 1/60 second is recommended for studio flash
Flash exposure compensation: can be set on camera up to ±2 stops in 1/3 or 1/2 stop increments; if flash compensation is set both on the camera and on a Speedlite, the Speedlite setting will override the camera setting
Flash exposure bracketing: possible with Speedlites 580EX, 550EX, MR-14EX and MT-24EX
Modelling flash: enabled with Speedlites 580EX, 550EX, 420EX, MR-14EX and MT-24EX; activated by pressing the depth-of-field button; provides 70Hz for 1 second
Wireless flash: enabled with Speedlites 580EX and 550EX (master or slave), 420EX (slave only), MR-14EX and MT-24EX (master only), and ST-E2 (master only)