I am currently creating a world in which the group in question is intended to ride reindeer rather than horses. The reasons for this aren't quite relevant, but they simply don't have horses available to most people unless they are extremely rich.
The reindeer in question are different from real-world reindeer, but for the sake of future questioners coming to find an answer, I will pretend these are real-world reindeer of any kind. Though, that info permits a tad of handwavium if it can be reasonably evolved in a semi-short timespan. The environment they are in, if applicable, is a mix of cold desert/tundra, taiga, and mountains.
They eventually gain access to horses more readily, but I was still curious if reindeers would make good mounts that could contend with horses in some manners. It is worth noting that these reindeer are domesticated, can have any riding gear that was available in the 15th century and prior or was plausible to create, and should be appropriate for casual use such as a draft animal or trail animal, if that helps clear up any cons or creates any pros. Bonus points if you can justify a reindeer as a war mount.
In conclusion, what are the pros and cons of using reindeer as mounts instead of horses?