The Christmas promotion is still on-going :

Enter promo code XMAS24 for 0.00105 BTC / GH/s! Only 28 TH/s available for today! Promo code valid until Dec 24th 23:59 (GMT+1)

100GHS for 0.105 should bring 0.008922/week and 0.03824/month (https://bitcoinwisdom.com/bitcoin/difficulty) theoretical ROI in less than 3months