There is one awkward quirk about BART's ticketing machines and Clipper...
Why can't it do more than just purchase e-cash value?
I use e-cash because it's universal and I can use it on any participating agency, but can't BART's ticketing machines be a little more flexible by letting passengers also purchase passes for other agencies?
A good example is the Millbrae station. Caltrain doesn't have Clipper add value machines at that station, so people can use BART's ticketing machines to add e-cash value. But the problem is that since BART shares that station with Caltrain, can't the machines also be able to purchase Caltrain's monthly passes and 8-rides?
Other stations like Daly City, Balboa Park, and Glen Park is also a transfer point for Muni, shouldn't the BART machines also be able to purchase Muni monthly passes too? BART stations in the East Bay are next to major AC Transit stops, why not allow AC Transit pass purchases too?
The point is: Clipper and BART, please make those machines flexible and allow passengers to purchase more than just e-cash. Muni metro ticketing machines and Clipper self-service machines can do it, why can't you?