The benefits of using FullStack campaigns are that these are lightning-fast. With the help of our SDKs, you can get the variation assignment without making any blocking requests to VWO servers. All the computation like deciding user eligibility for a campaign and assigning variation to a user is carried out by our smart SDKs. We use a hashing algorithm MurmurHash to carry out our bucketing logic.
The only thing that could be blocking is fetching settingsFile. The VWO SDK requires settings file for its instantiation. Either you can cache it or fetch it just after the server is up, if possible. See how to manage settingsFIle.
As there is no client-side custom code execution, using a FullStack campaign is much faster.