For what it is worth,
If it says Spyder on the box, or looks like one, DONT BUY IT!
As a tech, i have no end of Spyders with problems. I dont even have mine working any more!
I like the Ion, i have sold lots, and they are a good starter marker, you can add to, should you wish. The Proto Rail, is better, but costs £100 more (at approx £250).
I dont know where you live, but if you can get to Snetterton on Sundays or Wednesday evenings, then come and have a chat with the players there, and have a go with an Ion and a Rail (evewn have a DM5 in Stock).
I do reccomend to 'try before you buy. and if you can, buy over the counter, not over the net, at least you have a person to turn to if things go wrong (no offence to mail order shops intended - i just like people!)
Hope this helps.
Mark