Double velcro closures can adapt also fine to your foot and are more rigid as well as a little more supportive with a steadier fit over the whole shoe compared to velcro lacings.
Leather uppers made from unlined suede stretch around a full size (+- half a size). Though they might feel a little uneasy in the beginning the advantage is a higher comfort after the break in period due to conforming better to your unique foot shape. Naturally they come with higher breathability that helps preventing aggressive smells and keeping your feet cooler in hot weather.
Climbing shoes without a toe pad give your foot more space and comfort since the outer material can stretch better and adjust to your foot. If the intended climbing style or the skill level simply does not require toe hooking a lot, a toe pad becomes unnecessary but also the shoe more affordable.
Lined suede will stretch only around half a size, depending on the sizing even a little more. While the lining adds to keeping the shape of the shoe and providing a tiny bit more comfort, it also adds material between your foot and the rock. This leads to slightly less precision and potentially the development of an odor over time.
Some shoes also come with partial lining e.g. in the toe box only to reduce the stretch selectively. The advantage compared to fully lined suede might be costs and still better breathability and comfort in the rest of the shoe.
The claw-like shape of an aggressive downturn allows you to more efficiently cling onto steep and distant footholds. Since the foot is not in its natural position this shape might cause discomfort over time especially for untrained feet. These shoes excel in very steep terrain and provide the highest hooking capabilities making them the best choice for your project with overhangs and roofs.
The higher the level of asymmetry the more pressure is generated towards the tip of the shoe but at the same time forces your foot into a more bend position. This design sacrifices comfort and support for more precision on small footholds.
You can easily compare this to the different grips you are using for climbing holds: the lower the angle the more surface area you can connect and the more friction you can create. Think of gripping a sloper with the full hand, compared to smearing a big part of the sole onto the wall.
This also holds true for smaller features where you crimp up your fingers with a higher angle to create more stability in the grip. Now think of high angled toes within the shoe giving you the ability to stand on really small footholds.
The more tension is provided the more stability you have within the shoe. This increases the ability to put more pressure onto smaller footholds and keeps your foot in place while toe and heel hooking. A shoe with less pre-tension offers more comfort throughout the day and feels more natural for beginner climbers.
How much pre-tension a shoe offers can often be seen at the angle of the heelband towards the sole. Higher tension can also be created with the use of a stronger rubber. This might be indicated e.g. with dots at the back of the shoe.
A good mixture between flexibility and support are medium hard rubbers. These compounds offer good edging capabilities as well as enough adaptability to place a bigger area of the soles on the rock for smearing. The hardness and thickness of the rubber also plays a role for the sensitivity. The thinner and softer the rubber, the easier you can feel small footholds.
If and where the midsole is placed plays a major role in the support and sturdiness of the climbing shoe. It creates a platform where you can place your foot on and distribute the pressure from the point of contact to a bigger surface.
Most commonly the midsole starts in the toe box and might be as small as just an insert to support the toes up to a layer of fabric for the whole length of the shoe. Whereas it increases support it also logically lowers the flexibility at the same time making it harder to bend the shoe for smearing. This additional fabric also adds a thin layer between your foot and the rock reducing the ability to feel smaller features.
