Yes, the skybox rezzer is fully functional and you can try it out before buying the parcel.
The skybox control is located on the ground at one of the edges of the parcel.
The parcel needs to be owned by yourself. Click the skybox control to register. Once registered, you can use the control.
The skybox control has a Teleport-button that will teleport you into the skybox. Every skybox also has a Teleport-button that will bring you back to the ground.
You have to be the owner of the parcel at the point of registration. Once registered, you can change the owner of the land and still use the skybox control.
Only you can use the skybox rezzer.
The skyboxes have different sizes. Only those sizes that fit onto the parcel are available to choose from.
Make sure that building is allowed for everyone until the skybox is rezzed.
You can IM simformer for help inworld.