Firstly the Arp 2500 has always been my most wanted analogue synth, but completely out of my price range, even back in 1990.
I bought several modules last year, and although the learning curve is steep i have found so many amazing in depth tutorial on YT that i'm already using these modules and getting excellent results. The possibilities are endless with these modules, and you often get great results / sounds from mistakes, of course there are no presets, so i take a picture when i have created something really special.
Build quality is excellent considering the cost of these modules, and the sounds are so pure and rich, the only one negative which has been stated a few times is that the inputs and outputs are not physically connected to the case, so care must be taken when plugging in and out with mini jack connectors, this is a small price to pay and i don't personally see this as a negative, just something to be aware of.