depends on the question, but the OG solutions are complicated because they want to illustrate the concept behind the problem. If you are faster and more accurate plugging in numbers, go for it. But beware that if you hit a hard problem where plugging-in doesn't work, you'll NEED to understand the concept to do the problem fast and correct.
I would still read how they go through each problem for Quant in the OG, and learn some shortcuts from their methods... that's my 2 cents.