"6.1.1 Removable Link
The main power cut-off MUST be a removable link, which must NOT be in place unless the robot is in
the arena or under the supervision of a technician. A key or switch is not allowed.
6.1.2 Accessibility
The link must be positioned in a visible part of the robot's bodywork, fitted away from any operating
weaponry or drive, and this position must be clearly marked.
6.1.3 Covers
The link may be fitted under a cover, but the cover must be able to be opened without the use of tools.
6.1.4 Kill Switch
If the robot uses an internal combustion engine(s), the "Power" cut-off must take the form of a clearly
labelled "Kill" switch. See Section 7 for further details on engines.
6.1.5 Inverted Link
Robots in the heavyweight class that are capable of being driven inverted, having a removable link fitted
that is only accessible when the robot is the right way up, must have a duplicate link fitted in the
opposing panel, so as to allow the robot to be disarmed when inverted."

It's all there in the FRA rules

Poles are not used to remove links, even if a robot is out of control, they are just left to run out of power. These machines are far more dangerous than a boat with a propeller on it.

Using the custom link is fine, but far more effort than necessary IMO. In a FW a XT90 or EC5 work fine, and an 100/200A Anderson in a HW. Putting them under a small door held down by a wing nut is pretty common (We even use industrial velcro to cover ours). While people tend to bury their links inside their robots, the links on both our spinners are easily accessible and on the outside of the robot and we have never lost a link.

Side thought, if your custom link breaks and you can't fix it then you may be in trouble fitting a new link if you have some custom housing. Sticking with the standard links like everyone else has its advantages.