For Redmag offloads I’ve used 2.5″ SSDs in 2.5″ USB 3 enclosures. These provide up to 500+ MB/sec write speeds and they do not throttle even after 30+ mins of continuous write. Just get the right SSD. Crucial MX500, Samsung 850, WD Blue are all fine.
For Alexa LF/35 shoots, 2.5″ SSDs may not keep up if the shoot is over 2 hrs per day. Then you need NVMe SSDs which are notorious for thermal throttling depending on model.
But 2.5″ SSDs are fine for quick (Redmag) offload as well as transcoding to dailies off the SSD.
But for long term storage you need to get a spinning drive and/or a RAID. The new 16TB and higher drives are very fast and can write at 250 MB/sec till the half way mark.
4-bay Thunderbolt 3 RAIDs from Sandisk (previously G-Tech), LaCie, Promise are fast too. 400-600 MB/sec write. Some OWC RAID models are software RAIDs, which in my experience are fine, but some say they are unreliable.
The new 8-bay RAIDs from Symply are amazingly fast, and small with a great hard case included.
Offload from Red card to 2.5″ SSD, and simultaneously to RAID is very fast, and I’ve used Hedge write them at like speeds.
For even longer term storage, after all deliverables are made, consider LTO backup so you can recycle the RAIDs for another job.