Is there an Exchange to purchase some tokens?
No exchange yet but you can use the Nxt decentralized asset exchange to buy this asset 10966270007977442520 that represent IOTA.
Is this trustfull and secure?
The asset exchange is trustful and secure but you need to trust the asset creator (me) for redeeming tokens when IOTA go live.
I may provide collateral in form of BTC to an independent escrow if needed but until now no one asked so it looks like people trust me.