Complex sentence: Scratch-builders tend to be the top echelon in terms of skill and craftsmanship; they tend to be the most discerning when it comes to accuracy and detail and they spend far more time on far fewer models than a kit assembler.
Split into simpler sentences: Scratch-builders tend to be the top echelon in terms of skill and craftsmanship. They tend to be the most discerning when it comes to accuracy and detail and they spend far more time on far fewer models than a kit assembler.