The ignition switch on an immobilizer equipped bike has two 4 pin connectors vs one 6 pin connector on a non-immobilizer. There are other differences but that's easy to check. Immobilizer equipped bikes have an immobilizer label on the tank and the red immobilizer indicator light on the cluster flashes, among other things. AFAIK
, immobilizer and non-immobilizer keys look the same, though the immobilizer keys in the aftermarket have a removable chip.
Key making machines can duplicate an existing chipped key. But a new ECM will require a different chip, which significantly complicates things.
Ask the seller if the immobilizer ECM comes with a key. There must be some sort of workaround because programming the chip to match an unknown ECM is possible, but difficult. I don't know for sure but assume that a new immobilizer ECM comes with a chip matching key that is not cut. You take it to a locksmith and get it cut to match the ignition switch. The only other reasonable alternate is that the ECM comes with a key and a new ignition switch. But that creates problems of its own because the key must also match the gas cap and tail lock.
The K8 owner's manual states "Two ignition keys are originally registered to the immobilizer system. It is possible to add two more keys. The indicator blinks numbers of registered key when the ignition switch is turned on." I don't know what registration involves but it sounds like something that Suzuki does to the ECM, presumably when you send it to them. However note that K7/K8 use a different, more powerful ECM. This may not apply to K5/K6 and I don't have a K5/K6 owner's manual for E24/E2/E19 to check. Note also that the K8 manual says that the ECM should be replaced if all keys are lost. This implies that a new ECM comes with keys.
One nuance is that the E24 ECM may work better on an EU bike that has an aftermarket exhaust because of the lower back pressure of a non-catalytic exhaust.
P.S. I don't know where that page above came from because this
is what I see from that source. It's consistent with what I've previously said.