The Sonnet Breakaway Box is lightest and smallest. The 350 version comes with a 350W PSU vs. 400W in the AKiTiO Node and 550W in the Mantiz Venus. For a full list of Thunderbolt 3 enclosures, detailed specs, and reviews check
eGPU.io buyers' guide.
The Sonnet Breakaway Box 350 only provides 15W of power delivery btw. The 550 version is the one that can charge MacBook Pro. It has 60W PD, good enough for 13" MBP, slow for 15" MBP. Currently, the Mantiz Venus is the only eGPU enclosure with 87W PD. If you want to build your own Metal 2 external graphics development kit, take a look
here.
No boot screen. Off-the-shelf RX 470/480/570/580 should work in 10.13 via a Thunderbolt 3 enclosure (w/ TI83 controller). For those with older Thunderbolt-equipped Macs, Thunderbolt 2 enclosure such as the AKiTiO Thunder2 has been confirmed to work in 10.13.
Even though there's new drivers for more AMD cards, Apple made changes in 10.13 so that the same kext edits for Fiji and Polaris 10 GPUs don't work anymore. When the new iMacs with RX 580 get into people's hands, we may have new development for Polaris 10 GPUs in the Mac Pro tower.