Trap bar pullovers provide a unique stimulus to the upper back, shoulders, chest, triceps, and abs, and they force you to do pullovers correctly.
Here's why you need to start doing it:
One of the most common mistakes with pullovers is to overstretch at the bottom of the movement. The unique and semi-awkward leverage used for trap bar pullovers forces you to terminate the range of motion at the ideal stopping point. If you overstretch, you'll lose control of the weight due to the disadvantageous leverage.
Pullovers with the trap bar allow you to use a wide, neutral grip, placing enormous tension on the lats, particularly in the stretched position. It's also shoulder friendly.
Because of the hanging nature of the weight and the challenging leverage that's pulling away and against you, it takes twice as long to do each rep. Essentially, the trap bar exaggerates the arcing motion of the movement. The time it takes to move into and out of the stretched position is greater due to the size, awkward nature, and overall positioning of the load.
Because you're forced to slow down the movement – particularly in the stretched position – it takes additional stress off the shoulder joint while providing incredible stress to the surrounding musculature.
The level of grip and forearm strength required during trap bar pullovers is unusually high. In order to control the trap bar and ensure it doesn't twist in the hands, you'll have to use near max-effort crushing grip-strength.
The stimulus to the core and abs is higher than almost any other pullover variation.
The trap bar also provides a less stable version of pullovers in general. As a result, it improves motor control by forcing you to hone in on mechanics.
Trap bar pullovers can be done using the standard grip or using the outside frame for handles. Although they're somewhat similar, the latter method is more challenging and less stable due to the length of the bar and decreased leverage.