Gumtree is a very clean and functioning website, although it is riddled with scammers and spammers.
But if you are cautious and follow the necessary precautions, then you will be fine and can often sell items on Gumtree without a hitch. I recommend this website, just be careful not to get scammed.
I do wish that the approval processing times after posting or updating an ad was quicker than it is, but it's not too bad.
Regards,
Hudson