Low official fees and quick registration. A cheap addition when you are already filing in Vietnam and Thailand — provided the use affidavits are tracked.
Cambodia can validate patents already granted in Singapore, China, Japan and by the EPO, which is far cheaper than prosecuting from scratch. Worth checking before you file nationally.
Use declarations fall due at set intervals to keep a registration alive. Same trap as the Philippines, smaller market, equally final.
If Vietnam and Thailand are already on the list, the marginal cost here is small.
Customs recordal matters more than litigation planning.
The usual precaution: file in your own name before anyone local has a reason to file in theirs.