Two dumbbells, one squat, all gains.
Chest up, weight in your heels. Don't let your knees cave inward.
Holding a dumbbell in each hand loads your quads through a full knee bend without a rack or a bar on your spine, and because the weight sits low or at the shoulders, your torso stays more upright than in a barbell back squat. Your glutes take over at the bottom, controlling depth and driving your hips through to lockout. It earns its place as the squat you can do anywhere, hard enough to grow legs with nothing but a pair of dumbbells.
For building quads in moderate rep ranges, absolutely, and it is far easier to set up. The barbell wins once you are strong enough that holding heavy enough dumbbells becomes a grip and logistics problem before your legs are challenged.
At the shoulders keeps you more upright and biases the quads, by the sides is quicker to set up and usually lets you go heavier. Both are legit, pick based on comfort and what you have available.
At least until your thighs reach parallel, deeper if your heels stay planted and your back stays neutral. The bottom position is where the quads and glutes get their stretch, so do not cut it short.
