Need Info about Dongle , Want to buy

Hell to all.

I am new in Chiness Miracle section.

I want to buy Infinity dongle for Chiness Miracle. I have Infinity BEST and its working well.

I came to know that Infinity dongle support for one year, after one year need credit.
But want to know, after one year what will happend to my dongle. I can not work with future infinity update or not.
And one more , can I work with old infinity box software.

Thanks in advance