We are using this product in our lab to "weld" acrylic:
WeldOn has the following advantages compared to Hysol:
1. It's tensile strength is 17 N/mm2 while Hysol reports 13 N/mm2 if I remember correctly.
2. It's cures within seconds to the point of holding the parts together. Within the next hour, it cures completely.
3. It's transparent - looks better after applied.
4. It doesn't glue parts together, it literally welds them together, so it is completely water non-soluble.
Other than that, I think they both do their job and either of them can be used. WeldOn seems to have some advantages though. The fast curing can be a disadvantage for beginners because it doesn't give one much time to move the parts around into their perfect positions as it dries up pretty fast. Other than that, it's a great alternative to Hysol.