The expected hashrate of the Obelisk is 100 GH/s, which means that with a block reward of 20M SC/DAY the monthly revenue will be of 60,000 SC. The revenue will be higher in the beginning and is expected to get to 60,000 SC/month when 10,000 Obelisks will be sold. This is expected to happen by June 2018.
According to this calculation it will only take around 5 months to start earning some profit out of this hardware when calculated with current SC and Bitcoin price. Monthly income of $700 around from $2500 initial investment sound too good to be true but I am not claiming they are scam.
https://www.reddit.com/r/siacoin/comments/6k3gnj/obelisk_presale_is_live/Every unit sold comes with a $250 single-use coupon for future purchases from Obelisk. Each coupon can be used up to once, and can be applied to get up to a $250 discount on a single unit in a future batch. Only one coupon may be applied per unit.
edit: As of 10:00am EST, July 2nd, we have received payments for 600 Obelisk miners.
$250 discount in another unit rather than simple price discount in pre-order
, which is quite good marketing strategy
They have sold already 600 units according to them which is simply amazing if true.