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Lacing provides you with the best personal fit if you struggle with finding comfort with most shoes. Since they provide more comfort these shoes are good for a long day when you don't want to frequently take them off as they need their time to put back on. The laces might compensate excessive stretch and the shoe might feel more secure on microholds by restricting the movement of material. But be careful with toe hooks! With the usually small or missing rubber pad they are hard to place and wear down your laces or outer quicker.
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.
Small toe pads offer some protection to the forefoot. This makes climbing and toe jamming in cracks a lot more comfortable and increases the durability of the shoe. This also comes in handy when getting more into climbs where toe hooking or jamming is needed.
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.
A flat profile grants most comfort by keeping the foot in its natural shape. This is an advantage for less steep routes, multi pitches and beginner climbers. Having straight toes lets the shoe slide easier into cracks for better foot jams. These shoes can also provide the highest amount of rubber to create friction on positive featureless rock i.e. smearing on slabs.
A straight shape distributes the load from the front to the whole shoe. This results in a higher support of your foot and preventing the muscles to tire quickly. This is beneficial for a long day at the crag and climbers who do not have developed strong foot muscles yet.
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.
The big advantage of soft rubbers are the overall flexibility and generally the increased stickiness yet offer a moderate edging ability. This is best for overhanging routes to reach and stick onto far away footholds. Shoes equipped with these rubbers also allow for very good smearing especially in indoor bouldering, but can fatigue the muscles of your foot quicker due to the lack of support.
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.