They are all legit, but are different. I am using two of the three.
Jobslinger is a great way for Sassie companies to offer their shops collectively. It's been around for a few years. The free version I find adequate to notify me of shops in my area and of MSPs offering shops in my area that may be new to me. Presto is quite new. It has been out only a short number of months. It is an app supplying Sassie shops. It does so in a map as well as list version and can connect you directly to the MSP to apply for/accept the shop. They operate on the same idea with the same shops.
IC Pro is something I did not sign up for, but many have. About all I can tell you beyond the description is that it is a legitimate company.
Happily shopping Rhode Island and nearby Massachusetts and Connecticut