Yes, a union is a way to gather forces, not only in your company, but also in broader spaces. It's easier for a union (even of two) to ask to meet your local elected officials, to seek legal support, advices from other union.
It also has a tendency to yield corruption. Some would call it lobbying but in the end it's a counter political force because forces on the other sides exist already.
Not sure fighting fire with fire is the solution, a last resort.
I'm a director of my small company, and a member of UTAW. The union doesn't just help with employment disputes but also campaigns generally on improving working conditions for all, through things like health and safety and setting reasonable expectations for how work will be done.
Are you just an employee or also an owner in that company? If you are an employee only, having a union to back you up could be extremely useful if things ever go bad.
Only employee. Joining an union is too expensive for me though given the reward seems pretty small. My industry does not even have a proper union (in Germany) so I'd have to join a generic one (verdi) which doesn't offer enough perks for me personally.
He's the only employee in a 2 man company. How exactly do your think the relationship here is likely to be play out? IMO it is likely that he has a pretty good and probably rather personable relationship with the company owner. And quite likely has rather good bargaining power already given that he can double his employer's workload by walking out the door and it'd in all likelihood be a big headache to replace him.
If he can't leverage his power when he already represents 100% of the company's employees a union is unlikely to help.
That really depends on your industry and your union (and where you're based). My union doesn't negotiate my salary, I do. They do provide help with contracts, NDAs, legal advise and a bunch of other stuff and do provide salary guidance. They are also cheap at ~€475 a year.
Another larger union, which organises industrial workers, cleaning staff and generally people with less formal education, is almost twice the cost. They do negotiate at least base pay for the industries they represent. Many of the people they represent are often better off having their union do the negotiations. When handling negotiations it's obviously not only about money, but the unions do need to be able to provide at least raise in salary that can cover their dues, and sometimes they can't.