What are the key factors to consider when choosing a mini pump for my bikes stem, and how do I balance the trade-offs between pump length, weight, pressure capacity, and valve compatibility? Specifically, what are the pros and cons of CO2 cartridge versus traditional manual pumps, and how do I determine the optimal pump size for my stems internal volume and intended usage? Should I prioritize ease of operation, compactness, or durability, and are there any particular features or designs that offer an advantage in terms of reliability or maintenance? Moreover, how do I ensure that the chosen pump is compatible with my bikes valve type, and what are the implications of choosing a pump with a built-in pressure gauge versus one without? What are the experiences of users with different types of mini pumps, and are there any emerging trends or innovations in pump design that I should be aware of?