cowie

I'm glad it worked out for you in this instance. That is, you had traded two extra hours each way to fly on AirAsia and avoided a more massive delay (and other inconveniences) had you picked Scoot instead.

However, I am unsure if your suggestion to fly out of Senai in order to avoid Scoot out of Changi will render most travellers better off in most circumstances. Things to consider:

1. The odds are that Scoot will be on time (they average about 80 per cent on the A320 and 65 per cent on the B787, see https://www.flyscoot.com/en/on-time-performance) but you are guaranteed, in effect, a "delay" of at least two hours each way on AirAsia due to the extra travel time.

2. Sometimes the Causeway just jams up, adding hours to immigration clearance time. Often you can predict and avoid this, e.g. don't travel during the school holidays. But sometimes you just can't. Staffing levels, increased security due to "terror threats", random accidents shutting off entire lanes, alignment of the sun and the moon, etc. You might miss your outbound flight from Senai because of this. As I mentioned before, we cross the border by car often enough to know roughly what days/hours to avoid, yet once in a while we've suffered three or four hour jams on what is normally a 30 minute wait.

Having said all that, I'd avoid Scoot if there are other workable solutions (travel insurance, buffering for delays, one-stop flights via KUL, etc), but for these reasons I won't consider Senai as an alternative. The land border crossing just throws up too many unknowns. But YMMV.