Agree, normal user will not know. ISP will not let us know too. Simba home internet does not assign you your own unique public IP address; it uses Carrier-grade NAT (CGNAT) which means you share a single public IP address with other customers. Impact on corporate VPNs: You may face issues connecting to corporate VPNs if they rely on a unique, non-shared IP address. CGNAT doesn't directly slow internet speeds but can cause slower performance due to increased latency from shared IP addresses, potential connection limits, and bottlenecks during peak usage.
CGNAT is endemic in other countries, eg in Thailand all the providers have CGNAT by default and you have to pay a significantly higher fee to avoid it. Newer providers (eg simba, starlink etc) and providers in developing countries have no choice but to use CGNAT.
Another potentially more significant problem is if you use any software that does p2p (bittorrent, games, voice/video calls with telegram or whatsapp etc), as two users behind CGNAT cannot connect directly to each other the traffic has to be proxied through a third party server - depending where that server is the latency could be increased significantly, and because of the cost of relaying all this traffic the services will often reduce quality to lower their costs. As you can't peer with local users due to CGNAT, your torrent downloads will come from users further away and often be much slower.
Other problems are caused by the shared IP is being banned from services or forced to complete captchas. Services have no real way to differentiate between a NAT gateway with lots of legitimate users behind it, or a single malicious user. They also use tracking cookies to log if you've already completed the captcha check.
Also since a single IP from an external perspective could be multiple users, for legal reasons the ISP needs to log all of the traffic going through the NAT gateway, so that if faced with a court order they are able to track a single connection back to an individual customer. As this tracking is expensive and needed anyway, ISPs are more likely to try to monetize the log stream to recover some of the costs.
CGNAT equipment is also extremely expensive, and sits alongside instead of replacing the routing equipment so the cost of service is higher. This is either reflected in higher service fees, reduced service elsewhere (eg poor transit), or trying to sell information from the logs as an extra revenue stream.
The answer is IPv6. No CGNAT needed, every device has its own public address. If you're using an ISP with CGNAT for legacy traffic and IPv6 you will notice some things are much faster and work much better than others. Those faster sites will be the ones using IPv6.
