I've personally not added my tuning and overclocking stuff to any startup script for fear of an endless reboot nightmare - that is just a personal thing, I know most people have no problems( I run a script from terminal -feels far more geeky )

Im not sure that these swapon / swapoffs would be fine at startup, as if the microSD is not functional it will return an error at the first step and preserve the onboard swap.

The second step disables the onboard swap though; and I have no idea what would happen if the device has no swap available before it re-enables it in the third step. I do know that the swap is either not used or used very little at all directly after a reebot (hence no difference to startup times as there is very little to copy, takes lot longer if the device has been in use for a while) so it may not matter.

I may have a look at my scrpits and have it check that the card is available before continuing, I'll post back here if I do.