Can these straps be used on any Fitbit, or only the Fitbit Air?

These are designed specifically for the Google Fitbit Air and use the Air's proprietary clasp system. They are not compatible with earlier Fitbit models such as the Charge series or Versa series, which use different band attachment mechanisms. Check the Fitbit Air connector type before purchasing a strap from any source.

Performance Loop vs. Active Band: which holds up better in Indian summer heat?

The Performance Loop is a woven fabric band with more airflow: it doesn't trap sweat against the wrist the way silicone does during long workouts or in high-humidity conditions. If you run outdoors or train in a non-air-conditioned gym, Performance Loop is more comfortable for extended wear. Active Band silicone is easier to clean and more resistant to odour buildup.

Is the Elevated Modern Band suitable for formal office wear in India?

The Elevated Modern Band has a cleaner, less sporty profile than the Active Band or Performance Loop. It works well with business-casual and formal office wear. The clasp is smooth and the strap material reads as an accessory rather than a fitness tracker band. For court-facing or client meetings, this is the strap to swap to.