Rockshox Sid 120mm to buy or not?

[Me rida my bicycle]

I like the look of the RS Sid 120mm and I am considering getting one. Just something bothering me there's a lot of them for sale like new or used. 

Are they just 💩 or why do so many people change them? 

I have a Fox sc 120mm and just lus to change something but don't want to spend so much money and be disappointed then I'd rather just change the decals on my fork. 

Looking forward to hearing your opinion. 

Thanks