Appalling 4G signal strength. Disappointing!

Did you test drive a Three SIM card prior to purchasing a 30-day Smarty plan so that you could evaluate the coverage and performance to see if it met your needs? Sometimes such issues can be down to temporary work on a local mast or congestion at certain times of the day - you can use the Three coverage checker/ network status with your postcode...that might tell you if there are any issues currently.

Bear in mind, no network can guarantee 100% coverage since the signal is affected by many different things (buildings, weather, terrain, distance from mast etc) .. or I would recommend starting a webchat to see if Smarty can troubleshoot for you. I don't think that there could be a difference in the signal itself since Three owns Smarty but it is known that a network that is strong in one area, may not be so good in another. That is an inherent problem with mobile networks in general.

The good thing is you're not tied to a long contract incase the coverage is not meeting your needs.