[ryandrake]

Buyer availability really isn't a concern, especially for short term bills. I've never had even the slightest problem selling a T-bill one the secondary market. It's almost always as instant as selling 100 shares of a stock.

[lyrrad]

There were liquidity issues at many brokers for short term T-Bills in the days and weeks before the debt ceiling crisis was resolved last year.

Some brokerages may have better liquidity and/or prices than others.

It can be prudent to have multiple cash holding types in case there are issues with some of them.