The sample looks different once it is down and wet
A sealer sample almost always gets shown dry, indoors, under good light, and that is exactly where a glossy finish looks its best. Take that same sheen outside onto a stamped patio after a rain and it can feel like a different product, shinier than expected and slicker underfoot than the sample ever hinted at. That gap between the sample and the finished slab is the whole reason this question gets asked, and it comes down to what sheen actually is.
A sealer is a film sitting on top of the slab, and sheen is how much light that film bounces back at you. A glossy sealer lays down a smoother, denser film, which reflects more light and pulls more depth out of the color underneath. Matte and satin sealers do the same protective job with a lower-shine finish, softer and closer to how the concrete looks freshly washed than coated. This sheen question only applies to a film-forming cure and seal product. A penetrating sealer soaks in instead of sitting on top, so it does not carry a gloss or matte look either way, it just changes how the surface sheds water underneath a finish you already have.
The tradeoff that matters outdoors: traction
Indoors, sheen is a pure style choice. Outdoors, it stops being one. A glossy film over a shallow stamp pattern gets slick fast once water sits on top of it, and that matters most anywhere bare feet or wet shoes are common: a pool deck, a covered patio, a walk that stays shaded and damp longer than the rest of the yard. Matte and satin finishes grip better wet because there is less of a smooth film for water to sheet across.
The stamp pattern itself plays into this too. A deeper, more textured print holds grip better than a shallow one no matter what sheen you choose, since the low points of the pattern give water somewhere to go instead of sitting on a flat film. An anti-skid grit additive can be worked into either sheen level, and on a glossy finish in a wet-prone spot, it is worth asking for.
Where each one makes sense
For a pool deck, a covered porch slab, or any walk that regularly sits wet, matte or satin with a grit additive is the practical choice, and it is the one we point people toward when kids or bare feet are part of the picture. For a front entry, a formal patio away from standing water, or anywhere the look matters more than wet traction, gloss is a reasonable pick and it is the finish that shows off a stamped pattern's color and depth the best.
It is not a permanent choice
Sealer wears off over a few years no matter which sheen you start with, and that recoat is a real chance to change course. If a glossy finish turned out slicker than you expected, or a matte finish is looking flatter than you want, the next reseal is when to switch. Nothing about the concrete underneath locks you into one sheen forever.
The same decision comes up again every time a slab is due for a fresh coat, not just on the first pour. A family that started with gloss on a pool deck and did not love how it felt underfoot can move to matte with a grit additive at the next recoat. There is no penalty for changing your mind once the old coat has worn thin enough to strip and start over.