Pros
The company genuinely cares for it's employees, the company is small so it feels like a big family, most everyone there are great to be around and are more than willing to teach, they offer 24 hour shifts, tons of 911 experience, if you work in PSRFA's area (Kent, Maple Valley, Sea-Tac), you respond red (lights and sirens) to every call, you get frequent face-to-face contact with multiple fire departments, Tri-Med has a great relationship with the local fire departments so firefighters treat you as an equal in most interactions as long as you're respectful and decent at your job, there's also tons of opportunity for overtime.
Cons
I honestly have nothing really negative to say. However, you definitely need to look at this company as a stepping-stone - and they advertise it as such. Use it as the resume builder to get the dream job. Many come here to get patient contacts for medic school and PA school. The frequent contact with the firefighters have resulted in letters of recommendation from them for good EMTs. It's fantastic experience for the start of an EMS career, but you'll never get a significant pay-raise outside of becoming a shift supervisor.