I am going for multi of 10
It is a waste of your money; seriously. Perhaps you will be lucky once, but in the long you will lose so much money by playing parlays or multiplies; whatever.
In the top countries is no value at all; like for instance Holland. They will win, they will probably win big, but there is no point in taking the risk at 1.08 or 1.50 for a handicap bet. You could see it with Engeland and Denmark last weekend, major upsets when they did not win. The other bets are too risky for a combo, you will make more money taking them in a single.
But you should decide your own strategy, I wish you all the best!
Only play for me is Czech Republic. Huge win over San Marino, Ireland is without 13 players. Odds around 2.10 are worth taking big for me.
Oh, and the units thingie; 1 unit is for everyone else; like for daisy it is 50E per unit, for someone else it could be 10E or 10$, for another person it could be 5E. Units vary from 1 - 10; 1 - 3 is a low stake, 4 - 7 is a reasonable stake, 8 - 10 is high stake, in otherwise high confidence in winning the bet.