I also want to know getting the free router on upgrade to bt10 which one more worth?
		
		
	 
Depends on what you want to do.
If you want to sell the router to offset the subscription price, ZenWiFi BT10 twin-pack is more worth it even with the S$12 per month top-up.
Rough price in Carousell for BNIB units:
TP-Link Archer BE805: S$360
Asus ZenWiFi BT10 twin-pack: S$800
If you need a mesh solution, go for the Asus ZenWiFi twin-pack and pay the S$12 per month top-up.
If you want to keep single router for own use, then I tend to like TP-Link Archer BE805 a bit better as it has a faster CPU. But then Asus ZenWiFi BT10 will have more FW features and longer FW support. So both are okay choices.
The above is just my personal opinion.
Either way you are getting a superb recontract deal from M1.