Ease of Use
Very simple to understand and control! The added tactile controls do wonders for the usability of the Shruthi interface. Menus jump to display values when potentiometers are changed. A solid 90% of editable parameters are given unique, tactile controls, making a very fast interface for programming sounds. some features are a bit puzzling to me. i don't really understand the purpose of the "jam" function, and I would honestly prefer something like portamento controls instead (notably absent from the front panel), but overall a huge improvement over the original shruthi.
Price
very expensive 
the kit with the enclosure ended up costing me around $500. This is about 3 and a half times more than the regular shruthi. that being said I've found the editable parameter controls on the XT to make this a more viable synth to use live, so i haven't ended up regretting the added bones.
Availability
Still in stock as a kit at mutable as far as I can tell. If not, they tend to restock pretty regularly. Fairly easy build, knocked it out in a day.
Durability
I'm not IN LOVE with the acrylic case design, but it's easy to assemble, and seems sturdy enough if you treat it right. The pots end up being fairly solid, and have managed to withstand more abuse than some of my Roland stuff (pesky dr. sample pots)
Sound Quality
A lot could be said here. the synth shines in the bass frequencies, with the analog filter giving a suitably authentic and extreme sound. The digital oscillators allow for an enormous amount of waveform options and customizability. it's a great synth to make interesting and whacky digital sounds and then dial in analog filter edge to taste. that being said, there are some nasty aliasing issues in the higher notes on this synth. I've found it to be particularly difficult to program above C5, where the pleasing rough edges in the bass sounds become cutting and harsh in their upper harmonics.
Its interface allows for more digital/chippy sounds than you might see on a traditional synthesizer. There are some interesting possibilities contrasting lo-fi chippy material with the traditional synth filter. I've had a lot of funs blurring some chip sounds stylistically.
Aestetics/ergonomics
Very cool looking design! screen is bright and easy to read. the knobs look especially electronic legit, mess with them live if you want your friends to think you're v talented.
Size
surprisingly small. is as capable as something like the korg ms2000r, yet manages to be almost a quarter of the size.
Portability
Lightweight, size makes it easy to get around. requires a standard barrel type 9v adapter. no batteries or headphone out on this sucker.
Sustainability
seems like a one shot deal. build it and you're set. might have some trouble sourcing a few of the parts if they go bad, but mutable does a very good job documenting the build list.
Sync-ability
Very midi syncable! nearly every parameter is controllable. has a midi thru with is nice as well. no CV, but who really thought there'd be CV on this.
Compliency
Strictly DIN 5 midi as far as I can tell. no usb or w/e.
Integration
Has a simple onboard sequencer and arp with can be sent to MIDI out, can do some neat stuff sending CC messages from the knobs, and allows for multiple shruthis to be polychained for polyphonic shruthi stuff if that's your dig.
Ease of Modification
Very easy to modify! Some particularly useful mods are actually build into the PCB of the SMR4 MKII including options for changing the filter curve and style. The holes in the sides of the acrylic case are great for mounting extra switches and bits.
Personal Experiences
Replaced my regular Shruthi with this one, and I don't regret. Was admittedly a bit expensive, but the ease of use is such an important factor for me. It has eliminated so much time I spent menu surfing and is honestly just more fun. using this guy live is a dream as well,