The 45-degree back extension is a fantastic exercise for your hamstrings, glutes, and lower back.
The position of your body during this movement means that you can challenge the posterior chain through a greater portion of the entire range of motion (ROM) than on horizontal back extensions or RDLs. As such, it should be considered a staple movement for developing a strong, muscular, injury-proof backside.
Most people just grab a weight plate, dumbbell, or kettlebell to add load. That's fine at first, but your hamstrings and glutes should be able to handle way more than a 45-pound plate. Holding multiple plates is tricky to set up.
The most popular alternative is to try and load a barbell on your back. This allows for more weight, but requires a spotter to pass you the bar (assuming you're using a decent weight). But I find this back-squat rack position has other problems. Most people find their ROM suffers. Also, the bar risks rolling forwards onto your neck. Many also find it uncomfortable and stressful on their necks.
Hold the barbell with a snatch grip and load it with small plates.
This allows you to get a full ROM and also challenges the upper back musculature isometrically. This makes the exercise phenomenal for the entire posterior chain.
If you have particularly long arms you can elevate the 45-degree back extension on a couple of bumper plates to allow you to get a full ROM.
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