i would highly recommend using webspeed instead of the rest adapter. we started using the rest adapter because that is the recommend approach but eventually scrapped it and used webspeed.
a few major advantages to using webspeed over the rest adapter come to mind -
1. webspeed is far easier to install, setup and maintain than the rest adapter's whole java server, webapps mess. especially if you need to install the servlet engine (for example on unix/linux), setup the authorizations and tie it to progress. not to mention java compatibility and many other problems. in comparison, webspeed is a regular progress installation and configuration (that you would have to do anyway for the rest adapter's appserver).
2. you don't have that cross origin resource sharing (cors) headache with webspeed because the messenger is on the same web server host and port which will require alot of research in java and java servlets to setup. you won't find anything in the progress docs about it. even progress tech support had no clue. cors is also slower or less efficient because it requires the browser to send an additional http option request for practically every request it makes.
3. webspeed allows you to send back any data not just json, like, pdf's, word and excel files.
4. we started using the rest adapter in 11.3 which wouldn't allow you to get the client ip address (maybe this feature was later added) which we needed for our security. of course, you can get the client ip address in webspeed.
5. the rest adapter's drag and drop designer is really redundant since we have a single gateway (and i would think most frameworks would also) for all our services instead of creating and maintaining hundreds of api's.
i don't see any point in using the rest adapter.