Regarding security aspect, as for what customer can do: you can bring your device and put it in shared rack while support personnel accompanies you. Power/Ethernet and if keyboard/screen is needed will be managed/connected/wired only by support staff.
One can rent a whole rack if you want dedicated access. And 1/2 or 1/4 racks are available if fullsize is not needed.
That the price for 1U will tend to not be very competitive with renting dedicated servers (I can rent a server including hosting for that price) because the overheads to the provider of subdividing that 42U rack adds up. The point wasn't that the security can't be dealt with, but that dealing with it is one more thing that contributes to a higher cost per U if you rent 1U than if you rent quarter rack or more.
Regarding security aspect, as for what customer can do: you can bring your device and put it in shared rack while support personnel accompanies you. Power/Ethernet and if keyboard/screen is needed will be managed/connected/wired only by support staff.
One can rent a whole rack if you want dedicated access. And 1/2 or 1/4 racks are available if fullsize is not needed.