How easy is the guttering here to install?

I see you can buy the prefab lenghts, so do they just slot together, or do thy require a small weld

Go to any tin shop and they will make up exactly what you need and the prices are reasonable. Here is my system to keep the rain off of the neighbors yard from the small roof over the kitchen patio. I have two downspouts for "balance" since one is sufficient

Not all "welds" are created equal. The "stainless steel rain gutter" crew who initially installed rain gutters at our home in Isaan, used some sort of primitive torch, not a professional welding machine, to put sections of stainless steel gutter together at our building site. They did fairly well in terms of "slope" to the down spouts, but after 3 years ALL the "welds" failed and one section seemed to have dropped. It's been a challenge to get a good crew to fix the original problem, but the key piece of advise I would have is ask to see how they "weld" sections together PRIOR to making a purchase. Every time I see that "rain gutter man" doing his day job as a guard in the parking lot at a Government Hospital, I realize why he keeps his "day job". Thailand is full of professional rain gutter firms, our builder did NOT direct us towards such.

Decided to go for the plastic type at home, as it was aesethically pleasing, and so easy to install.