The difference is rallyrd immediately puts your money to sleep for 90 days post-IPO, and then they only let you trade shares one day a month following the lockup period (better hope you don't need your money in a pinch). Their website is as bare bones as you can get (no past results, no current offerings, just "Try the app!"), and as several others have pointed out, they have a lot of small print aimed at avoiding any type of liability.
The concept of fractional ownership is solid. The execution by rallyrd is abysmal.