First, let me say I am not a fan of the poly glues primarily because I have found no advantage to them over standard PVA glues when gluing wood to wood joints except for gluing oily, exotic woods. "Creep" is much less of a problem but there are other adhesives that are creep resistant such as plastic resin and hide glue. I'm sure there are other opinions however.
That said, like any PVA glue (white or yellow) the poly's are no stronger than the wood itself--and may be weaker if they are not used correctly. They cure by a reaction with moisture but many use too much adhesive and moisture. Excess moisture increases the reaction but shortens open time--one of their claimed benefits--and results in excessive foaming and a weaker joint. If the wood is at a moisture content of 10% or more, additional dampening is probably detrimental, not helpful. There are now PVA glues with extended open time. In fact the white PVA has virtually exactly the same open time as the poly. The yellow PVA was formulated originally to respond to woodworkers who wanted a faster setting adhesive. Strangely, some poly glues are now being marketted that have a shorter open time and faster cure because some wood workers have complained about the longer clamp time required for the original polys.
Some poly adhesives are certified to meet the ANSI Type 1 waterproof standard which means they can be used for totally submerged applications. However, for normal, non-submerged outdoor use, a type II adhesive will work as well.
While "gap filling" they fill gaps with foam which has no strength. The adhesive expands as it cures tending to force glued surfaces apart so tight clamping is required. They also require that the clamp pressure be maintained for much longer than most other adhesives.
It contains hazardous materials and should be used in a ventilated area and kept away from skin if you believe the Material Safety Data Sheet. If it gets on your hands, only time will will remove the stain.
Finally, they cost much more than other glues and IMO, do not offer many advantages over less expensive adhesives.