Stock price when the opinion was issued
Now paying 15-20 bps higher than a plain-vanilla high-interest savings ETF. Good if you need access to cash, never drops below where you bought it if you buy on the ex-dividend date. A cash-like position in your portfolio. Pays interest.
The sawtooth graph is explained as money accumulating on short-term paper holdings, and then paid out all at once every month. You can, of course, automatically reinvest the proceeds.
ZMMK and ZST are his two favourite BMO ETFs for money market exposure. He uses both in the bond fund he manages. Which one you chose depends on your risk tolerance. Both are excellent, look at both.