Me...
1. Strength: can hold up to 121 lbs (55 kg) although 100 kilos might be good enough. Depends on manufacturer, model, size, material etc
2. Lightweightness: titanium or carbon fiber etc for the Mercedes model and something cheaper for standard model (hardened stainless steel?)
3. Durability: lasts more than 5 years with non-stop use, perhaps replacing some minor hardware
4. Flexibility: Not brittle, has to have a little 'give' in case used as a swing
5. Versatility: optional configurations, examples - height and depth. Can use as a sex swing also (with adaptations, to lower cost for simple stand model)
6. Modularness: can take apart into multiple pieces
7. Portability: can fit in a car trunk or duffle bag and taken on bus without injuring anyone.
8. Non-proprietariness: easy to get replacement parts
9. Good value: Not expensive for standard model, under $200 in Canadian market. Luxury model under $350.