Are new mobile plans like Grid Mobile be reliable to transfer to? Do they offers with have trial periods?

Grid Mobile Referral code: GRIDLEO

Signup process was really quick, switched from M1 to GridMobile and number was transferred instantly. Did not experience any downtime so far. Signal strength is also very strong in tunnels. They are using Singtel's infrastructure too.

Use my referral code when signing up, currently they have a promo for 30GB for $17.90/month.

These new companies are mobile virtual network operators. What they do is to lease the network infrastructure from existing companies (Singtel, Starhub, M1) to provide it's services. The network/receptivity issues at certain areas which these big 3 companies will likely carry over.