Servo is the brand, but they all have similar motor drives. I have two newer Align AL-500 power feeds on my mill, no shortage of power and they are very well made looking at the components, switch gear and the drive gear is brass. They are made in Taiwan (no plastic) and a bit more common than the no-name ones often sold on eBay, so there are parts for the current versions. I have no expectations as to getting parts in 10-15 years, if they last that long than I am fine with the money spent. I will get some spare brushes and maybe a drive gear assembly at some point, if anything more than that it probably doesn't pay to repair them. The Servo drives are very nice and the price matches that, so in the industrial setting it may be warranted. As a hobbyist I just couldn't see paying 2-3X more than the Align drives for the Servo drives. Also when it does come to repair the Servos, it is often very expensive. I had looked at a few used mills from an industrial setting, and often they had a dead Servo drive, granted they had a hard life. If I could afford the Servo drives, I would buy them, maybe when my current drives go I will reconsider it.
As far as I am aware almost all these drive units including the Servo use Zytel (nylon) gear at the bottom of the units. This may act as a sacrificial gear if the drive is over driven. The type and quality of the bevel gear may be another matter.