If they’re designed and machined correctly then absolutely. The rigidity of the upper can increase in the sectional area around the barrel extension receiver(part where the barrel mates into the upper). You also increase the accuracy of the system setup with iron sights as the arc radius never changes between the front and rear sight. This is because there is zero movement between the upper mounted rear sight and the handguard mounted front sight.
But also, if designed and machined correctly you can shave some weight off the MU vs a standard upper and similar handguard. 99% of aluminum handguards are made from precision extruded aluminum cores(proprietary) then machined on turning centers/mills/EDM’s to achieve the final product. Without needed to bolt/affix the handguard to the barrel nut, the MU can be made lighter as there’s no fasteners, a lighter barrel nut(potential) and lighter material use near where the handguard would normally clamp/bolt to the barrel nut or comparable bracket.
downside…price and lack of “interchanability” of the MU design.