If you are even slightly unsure about your soldering abilities, get a solderless chip. Modding a PS2 is an advanced to expert level soldering job requiring a lighted magnifying glass and a very good low wattage soldering iron with a very small tip. Not for the faint of heart.

I have a solderless chip and it is fantastic. There are some mixed testimonials out there, but it is relatively easy to do, and if you can solder in the first place, you understand patience and delicate movement. Just make sure you study the instructions carefully before doing anything and have some electrical tape and/or hot glue ready to make sure everything is properly insulated. The toughest part of the whole job with a solderless chip is disassembly and careful reassembly of the machine. A PS2 is a complicated beast.

Also, a very important word to the wise. If you have a V9+ PS2, you are going to need to desolder one pin on one and solder it to a +5V point to avoid blowing the chip that powers and runs the DVDROM and drawer mechanism. It is prone to burning out with the increased load a chip adds. One wire isn't so bad actually and it is in a place that is easy to work with. Look up "Romeo Mod" for more info.

I waited until the solderless chips came out, and I'm incredibly happy with the versatility of a chipped PS2. It is worth the time and effort, especially when you can cheat with the solderless. As for the DMS, you don't need to spend the extra money on the additional onboard chip memory unless you want to make using homebrew/hot coffee easier.

Best of luck!