Well, the Birdy can also a produce a symphony of squeaks and rattles. Some of these irritations can be quickly diagnosed and rectified; others prove to be more elusive, and some are just downright recalcitrant…
You can tune the suspension by switching both the front spring and rear elastomers. In addition, you can use different width tyres to adjust the feel of the ride. That said, pot-holes and small-wheels (particularly on even smaller wheels than you are used to on the Mu SL) are always a bad combination.
The Birdy will provide a softer ride than a Mu SL, and as the roads you are cycling on sound unforgiving, it might be worth considering a fully-suspended folder.
The R&M Birdy will also fold smaller than a Jetstream XP, but not significantly so. If you went for the XP (and the 2007 model sounds like a good all-rounder) you would also get more tyre choices in the ERTO 406 size.