First of all, engineered floor joists are very common and very sturdy. In fact, they totally beat out typical floor joists in almost every way - pound for pound.
They are basically two strips of wood with OSB board in the middle. It seams like that would not be very strong, but it is. Just like plywood is stronger than a straight peice of wood, so engineered floor joists are better as well.
There are some things to keep in mind though. WHile moisture resistant, if they do get damaged they are vexpensive to repair. Also, there are usually pre-designated penetrations through the floor joists. Making an opening bigger than the one already designated or making an opening in another location can be structurally damaging.
All-in-all though, engineered floor joists are a great product that should work well for years to come!