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[The Fifth Horseman]

I noticed that if you shoot down a lot of UFOs the first week, for second week you'll be facing transports and fast attack ships with shields, so just downing a single scout and a single proble can actually help you keeping tech advancement down. The down side is of course that you'll have to do a lot of missions vs non-equipment aliens (worms, spitters, brainsuckers), so you don't get cash from the tactical battles.

Actually, the game adapts to your score. If you play a lot of Raids and get a high score before the first UFO appears, you can encounter Personal Shields and Devastator Cannons in your first mission.