Several points in this long post:
I use the Metabones Mark IV and the Fotodiox Viselex ND Throttle adapters with my Sony A7r. The ND Throttle has a built-in variable ND filter, is designed for Canon lenses only as far as I can tell, but it eliminates the issue of vignetting with wide angle lenses, supports only manual focus.
The Metabones adapter works well either handheld or tripod mounted. I always use focus peaking (Red is my preference) and have been able to nail focus even when handheld. For the most part, only use Metabones AF when on a tripod because it is slower than manual. The A7r has several neat focus aids such as focus zoom and focus peaking. I have found that I prefer manual focus for most of my shooting, especially when handheld. Focus peaking is a key!
Have never had an issue changing lenses with the adapters. Once the adapter is mounted to the camera, changing lenses is the same as if there was no adapter (hit the lens release, twist, insert next lens, twist on).
I purchased the Sony-Zeiss 55mm f/1.8 lens for use in shooting panoramas with a Panosaurus 2.0 Pano head (on Amazon). Great lens. When I need other focal lengths I use my Canon lenses with an adapter, but generally avoid changing lenses because you have to find the nodal point for each focal length and the pano head is marked for the Sony lens.
I simultaneously use two L-Brackets on the camera and the Metabones adapter (unless the battery grip is installed, then only use an adapter on the Metabones). This allows use of Arca Swiss plates and use of large lenses with the diminutive A7r body (wouldn't want to hang a heavy lens off the camera, would rather hang the camera on the sturdily mounted lens). The $37 Desmond L-Plate bracket (for the camera body without battery grip) is available on Amazon
http://www.amazon.com/gp/product/B00AR04OI2/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1 and the one I leave on the Metabones adapter is the $99 Hejner Photo Sony NEX 7 bracket at
http://www.hejnarphotostore.com/index.php?main_page=product_info&products_id=183&zenid=d7pgrtcias5rd2felku6an38k5 This setup allows you to remove the Metabones adapter and still have an L-bracket.
I recommend that you purchase additional batteries since the A7r has a small battery and it consumes a lot of power with its EVF and electronics. Can endorse Wasabi Power (versus expensive OEM) $27 for two batteries and a charger (not a typo) on Amazon
http://www.amazon.com/gp/product/B0049WBZEK/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1Because the A7r camera burns through batteries so quickly I use a Sony VG-C1EM battery grip (kit has additional goodies) at
http://www.amazon.com/VGC1EM-VGC-1EM-Camera-Batteries-Accessory/dp/B00HNEQ9F6/ref=sr_1_1?ie=UTF8&qid=1407173132&sr=8-1&keywords=sony+battery+grip+a7r It's pricey, but necessary in my work. There is an entire post on today's UHH about using a grip on a mirrorless camera. Appears to be comments by many people who don't own a MILC and a grip. It isn't only about weight when going the A7r route.
I am really pleased with the Sony A7r despite some of its shortcomings (the biggest is that it only shoots jpeg when using some of the cool features).
Feel free to contact me at tm2guy@gmail.com if you would like additional info. Name is Gary.