The single velcro strap keeps the foot in the shoe fixing the issue of slipping hooks while still providing a versatile freedom in the front. However a good fitting in the toe box is still harder and more dependent on your foot shape.
Synthetic materials tend to not stretch at all keeping the shoe in its shape for longer time and eases the sizing of your shoe. If it fits, it sits! These materials are also preferred by many vegetarians and vegans. A downside is the lower breathability and therefore higher hygienic care.
Good toe hooking is offered by climbing shoes with medium sized toe pads. These higher performance shoes protect the forefoot well while still being able toe stretch in the sides to a certain extend.
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.
Moderately downturned shoes are the best choice when looking for an allrounder combining both comfort and performance. The slightly arched profile generates more force into the toe section as well as the heel supporting better edging and heel hooking. These shoes are best worn for climbs ranging from a vertical face to slightly overhanging routes.
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.