When evaluating a flexible cystoscope, you must prioritize the outer diameter (OD) and the working channel diameter. For adult diagnostic procedures, an OD of 5.0mm to 5.5mm is standard, while a working channel of 2.0mm to 2.2mm is essential for surgical instruments. Additionally, check the angulation range; top-tier models offer up/down deflection of at least 210°/120° to ensure full visualization of the bladder neck. Finally, verify the image resolution, prioritizing CMOS sensor technology for high-definition (HD) clarity without the need for bulky external camera heads.