If you don't already have a QAT device, I would not suggest getting one
specifically for Tor. In particular, Tor doesn't spend very much time
actually doing AES. It's mostly overhead from cell processing, TCP,
small packets, etc. Additionally, because Tor uses a large number of
relatively low-bandwidth connections, it will mostly send small chunks
to the hardware engine, which is not particularly efficient. In the
future, it may be possible to use KTLS, in which case QAT might actually
improve performance quite a bit. However, there are a number of blockers
to this, including that it messes with Tor's bandwidth limiting.