For some patients this incision is ideal and can provide very natural looking results. Be sure to ask for many photos of patients who have had their implants placed through this incision, and then speak with some patients and what their experience is like.
A surgeon with expertise at transaxillary (through an underarm incision) breast augmentation should be capable of producing natural-appearing results with that approach. Insist on seeing a large number of 'before and after' photos of your surgeon's transaxillary breast augmentation results (including the surgical scars) before you agree to have that surgeon place your breast implants via that approach.
Some patients have a starting point that makes it challenging to achieve an ideal result through an underarm area incision. Both of the 'before and after' images you attached show patients with a very low NAC (nipple-areola complex) position on the breast mound, and I almost never offer a trans-axillary approach to those patients. The first patient has almost no lower pole breast tissue preoperatively, and needs to have her inframammary fold (IMF) lowered significantly to achieve a natural-appearing implant position. I only do this (significant lowering of the IMF) through an IMF incision.
The second patient has a very low NAC position preop and appears to need a lift in addition to augmentation. Both of these patients' preoperative breast types are a setup for a distinctly unnatural postop appearance when the surgery is performed through an underarm incision, and unfortunately that is the result that both of them got. So the axillary approach is not for every patient (or surgeon).
Another mistake that is often made through the axillary approach is non-release or inadequate release of the inferior origin of the pectorals major muscle. If the inferior origin is not released, then the pec major muscle holds the implants high and prevents them from settling into a natural position.