I'm thinking that the CatBus would be a good project to paint entirely with acrylic paint pens. Recently, I've found them really useful - no messing around mixing paint and then cleaning up the brush. Perfect for the time-poor modeller who can see a deadline approaching. The speed the paint dries is another help here.
To date, my tools have been from Ammo and MiG, proper modellers products, but at my club, the chaps working on the modular layout pointed me at this pack on Amazon. They are getting on well with them, and for the price, an experiment wasn't going to hurt.
A benefit is that this provides a lot of different colours, which may be helpful for figure painting where I need a tiny bit of colour, but am too stingy to splash out £4+ on a tinlet of Humbrol. I might love purple, but I doubt it would have gone off by the second time I opened the pot.
The pens are normal pen size, and have a brush end, and a "pointed" one. Oddly, the brush is the more pointed of the two. Another moan (this is the internet) is that the pen doesn't say what colour it is, you are left to compare it to the back of the box and guess.





