Is that for a Ford one? They were going for silly money for a while.
I heard of some people having problems with cheap non-Ford ones, causing a drain on the battery etc.
But for £50 it could be worth a punt

Because the Ford ones were getting so pricey there's a guy on eBay who will bore out your original one to 60mm and fit a new butterfly for about £100, which is what I had done a few years ago. The gearing in mine that I had machined has recently become quite noisy though although that could just be wear and unrelated.
(Never mind, I just looked - it seems he's doubled his price since then)

To be honest though I noticed no difference in how the car feels when swapping back to a 55mm one.