I thought I'd share a few discoveries.
I've just started to learn about Array formulas.

Sumproduct rule:
=SUMPRODUCT(--MID("123",{1,2,3},1),--ISNUMBER({1,2,3})) -- 6
=SUMPRODUCT(MID("123",{1,2,3},1),ISNUMBER({1,2,3}) ) -- 0
=SUM(MID("123",{1,2,3},1)*ISNUMBER({1,2,3})) -- 6
="1"*True -- 1

Numerical arrays treated as text:
=SUM(--ISERROR(FIND("2";ROW(2:5)))) -- 3
=SUM(--ISERROR(FIND("2";COLUMN(B:E)))) -- 3

Text array
=SUM(--ISERROR(FIND("B";CHAR(COLUMN(B:E)+64)))) -- 3

A good tool to see what Excel is doing:
Mark a piece in a formula at the Function bar and press F9. Esc or Enter

Ola