This should be in the techroom, so if it disappears from here you should check there.
The two guns you have mentioned are quite different beasts. The Timmy is reliable and efficient. The DM5 is a little smaller, less efficient but a little softer on paint and has less kick.
If I were to choose between the two, I would pick the DM5, because its worth more money than the timmy and its easier to get spares for.
Also, the old timmys had really bad boards, even some of the aftermarket boards had awful problems with bounce. There are a couple of decent boards for it like the tadao, but thats might cost you.
If you really dont want to bother maintaining your gun, then the timmy may be the best choice, because its more likely to keep running without routine maintinence unlike a DM. But if you dont mind lubing the bolt every once in a while (or sending it to one of the many competent DM techs we have in the UK) the DM5 is probably a better option.
£350 for the DM5 and hopper isnt a bad price, but the new DM7 is out soon, so do a couple of searches on classifieds to see what prices other DM5s have sold for recently.
