If you phone could get a good connection on Maxis network at your location, then this MaxisOne Go Wifi will be 99.9% the same as your postpaid/prepaid plan. Furthermore, 4G CPE router tends to have better connection than any phone does. The only issue is whether or not 300GB quotas enough for your monthly usage.
I may suggest you take the SIM only since there's no contract. You are allowed to purchase the 4G router for RM1 later but it'll tie you to a 12-month contract.