1) Key requirements for oxygen concentrators include using a 16A socket with stabilizer, avoiding extensions or power cords, and models that output at least 93% oxygen concentration. 2) Recommended brands are Philips, Airsep, Dr. Diaz, and Dr. Trust due to their plastic quality, design, and service support. 3) Important factors when choosing a brand include the warranty length and whether onsite service is provided, as sieve filters may need replacement after a period of time.