LocalTalk Bridge and LaserWriter Bridge are fairly old and haven't been updated by Apple for some time. LocalTalk Bridge 2.1 is not completely compatible with Mac OS 8.5, and no update to this product is expected. Asante and Farallon both make such adapters. How you connect more than one Mac to high-speed Internet depends on what kind of account you have.
Software routers are less expensive than hardware routers, but are also more complex to set up.
If you connect the incoming signal to a second Ethernet port, it will only see the second port, keeping your other Macs secure. Sharing the Internet connection may violate your service agreement, and the provider may choose to disconnect the service. If you connect more than one Mac to a hub without additional IP addresses or a router, the first Mac that powers up will grab the available IP address. Any other Mac that powers up afterwards won't be able to use the IP address, since it's already taken. In order to make this kind of connection work, you usually need to switch both Macs over at the same time, so both Macs will send signals to each other.