If you wait long enough, a better platform will come along.
If you wait even longer, an even better one will emerge.
The cost of picking the wrong one is high. So better to wait until you've got the best one right?
But what's the cost of not having a community all this time?
What's the cost of not connecting people around you, your organisation, or their passions?
What's the cost of a competitor launching and growing their community before you?
More directly, what's the daily cost of not increasing customer loyalty, knowledge exchange, and increasing donations?
I assume you're building a community because you believe that the benefits outweigh the costs. In which case, every day you delay is a lost benefit that becomes an additional cost.
Picking the wrong platform for the community might be expensive. Not having a community is definitely more expensive.