We use Sonicwall routers/firewalls fairly often for client setups. I tend to find them to be a good blend of price, functionality, and ease of use. I won’t go into any long sales pitch on them, but needless to say I spend a fair amount of time setting up and using them. For small office setups, there is usually no need for redundancy in firewalls, but as soon as the office grows to a reasonable size where long internet downtime can’t be tolerated, a redundant firewall quickly becomes necessary.
Sonicwall’s Stateful High Availability configuration provides a good solution to this. By purchasing a high availability unit of the same model (usually runs just slightly cheaper than a regular version of that model) and a Stateful HA license (depends on the model, but usually $300 to $600), you should be good to go. The only other items you will need are either a cross over cable and a small switch (you only need 3 ports) or 3 ports separate carved out of a large manageable switch (to split the incoming internet connection between the two Sonicwall units).
The main benefit here is that one of the Sonicwalls can completely fail, and the other one will have the internet up and running again, usually in about 2 seconds according to my informal tests. Another benefit is that it allows for one Sonicwall to be restarted at a time without taking the internet down, which is useful for firmware updates or anything else that requires a restart. One more advantage is that if you plug each Sonicwall into a different switch (assuming you have more than one core switch), it will allow for a switch failure while keeping the rest of the network (everything not attached to that switch) up and running.
We recommend the Sonicwall High Availability Configuration and are happy to assist implementation for your business.