An extra ranger or soldier does not compare to having access to new building or unit types. I would caution against purchasing these tech slots as they are of diminishing value at higher levels. Mercenaries I and Mercenaries II will make the first five minutes of a mission much easier. You will have an easier time getting resources (wood, stone, and oil) at the start of a mission. An extra ranger, soldier, or sniper can allow greater map control. For a small amount of research points you can purchase technology that provides you with additional starting units.
The first technologies available to you look excellent on paper.
