What’s the difference between Avantree’s multiple headphone sets?

Shift:

• Connect multiple headphones to the same TV
• Comes with two headphones (supports up to 100)
• Comes with two transmitters (supports up to 3)
• Only Shift headphones can be added
• Switch between TVs easily with the channel switch function
• 2.4g wireless technology

Quartet:

• Connect multiple headphones to the same TV
• Comes with four headphones (supports up to 100)
• Comes with one transmitter
• Only Quartet and Duet headphones can be added
• Cannot switch between TVs
• 2.4g wireless technology

Duet:

• Connect multiple headphones to the same TV
• Comes with two headphones (supports up to 100)
• Comes with one transmitter
• Only Duet and Quartet headphones can be added
• Cannot switch between TVs
• 2.4g wireless technology

HT41899:

• Connect multiple headphones to the same TV
• Comes with two headphones (supports up to 2)
• Comes with one transmitter
• Any Bluetooth headphones can be added
• Cannot switch between TVs
• Bluetooth wireless technology