I used zip ties all the time with no problem but changed to a small spider because fishing out the bags was a pain in the ass. Was adding bittering hops and then fishing out the boiling hot bag to add flavour hops at 30, 15 and 5 min not workable. The spider makes sense to me. I do still use the nylon zip ties when I need to dry hop a beer.
I use a separate bag for each addition. I hang them from a spoon laid across my kettle so they're freely suspended and I don't have to fish for them afterwards.