I won this item from the Bathhouse and it has the option to "use item". What will happen if I use this item? Thank you

You get some SP

It gives you a random amount of sP. I don't know what the range is on it, the most I've gotten was around 100k, once. It's usually less than the SS price but I don't think I've really seen it besides as a Bathhouse prize so I usually just open mine since I don't expect it to sell fast

Thanks for sharing your knowledge and methods with me,

I was waiting for a Vesnali Monday so that Use-ing a bunch of Money Trees would get me flowers and a chance at Tempest.

I opened forty of them and wrote down the sP I got. I didn't mark down any sP lower than a thousand. My results ranged from 1000 to 49000sP. Average was 24100sP which is what the usershop price is (or was, before I bought forty of them). There is no skew, so it appears to be purely random and not some goal number plus or minus a bit.