Fixed wireless is very different to mobile broadband. The antenna is installed with reasonable signal, which usually requires line-of-sight. With a clear line-of-sight there is nothing to affect the signal strength in the same way as 3G would be affected.
As the ISP is using nanostations M5's then they will likely be using 5.4Ghz or 5.8Ghz which are used for outdoor fixed wireless. Therefore the service should not suffer interference from normal home Wi-Fi in 2.4Ghz and 5.2Ghz.
Fixed wireless can actually have better ping times than ADSL if backhauled to the internet over fibre (leased line) pings could be as low as 5~10ms.
What's the Wireless ISP you are looking at?
O2 Broadband Premium LLU
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