As andrekua2 said before their ZTE MC801A from Celcom that is based on SDX55 wasn't that good. ZTE MC801A was released on 14 Nov 2019, so hopefully it is better for the newer generation products. Still, looking online for specs of the ZTE G5B there are a lot of different spec lists. I would trust the specs if it comes with a more official looking PDF file. The specs for the H153-381 is more widely known. I think I'm leaning more to ZTE G5B with our current ericsson infrastructure. If issues surfaced during the 2 years contract period, do complaint through MCMC and get a replacement.
After the contract period ends, or even before you guys can refer to videos on youtube to mod external sma antenna ports to replace the internal antenna. The PH 5G home wifi community seems quite active in their modding of the H153-381. Can refer to some youtube videos for that. As for the ZTE G5B, I haven't found a specific website or any posts with mods to it. But if the ZTE MC888 that are similar in form factor can be modded, I would bet the ZTE G5B will also be possible to be modded.
ZTE G5B might also be called MC888B, also it is very similar to a normal MC888. The difference are the new 'AI' antenna inside the ZTE G5B for better signals, the exterior looks identical.
The rationale for choosing the H153-381 based on the Balong 5000 would be better suited with the 2nd 5G network using Huawei and ZTE systems. But by then you should get a better modem with higher carrier aggregation. The upcoming SDX75 5G module is capable of 5CA, I think both the ZTE G5B and H153-381 are theoretically capable of 2CA. Routers based on X75 are already available now but the Quectel RM551e-GL 5G module (SDX75) is still in the engineering sample phase.



Pics sourced from router-mods.co.uk/product/zte-mc888-5g-cpe-router-modification-services/