For me, I needed something to securely take crampons for approaching alpine rock routes over snow slopes or glaciers. As I was likely to end up carrying them on route, I wanted them as light and compact as possible. My alternative to new boots was to use my Sportiva Trango Tower Extreme GTX boots so I needed something sufficiently lighter and more compact to justify the expense.
I've tried full strap on crampons on bendy trainers in the past, but bergshrunds, steep neve and the inevitable bits of rock climbing in this set up all get a bit too exciting for my liking, so I needed something stiff enough for a secure fit.
I ended up with a pair of Dolomite Veloce GTX shoes and Petzl Irvis Hybrid crampons with a combined weight of just over 1.5kg.
I tried the shoes out in the Lakes, walking up Sticks Pass, Helvellyn, down Striding and up Swirrel Edge then down to Thirlspot. They felt more like a boot than a trainer but I quickly got used to how they felt and had comfortable feet with no rub points. Admittedly, my normal Salomon trail shoes would have been a bit less tiring but I was happy.
In the Alps, I used an old pair of trail shoes for the first 3 approaches and the snowy descent off the back of the Dibona was a bit silly! I should have worn the Veloce with a decent edge / heel! By the time we'd walked back down to the car carrying a sack with rope, rack etc I was feeling all the stones through my soles.
Next route up was the Badile, with the 5 3/4 hour walk up and down to the Sasc Fura hut plus another rocky hour to the bivi. The Veloce were perfect giving some ankle protection from knocks, cushioning from the rocky ground, firm support on the scrambling and metal rungs and a good edge for kicking into the mud and grass. (It's not a great hut path!). There were two sizeable patches of hard neve (at 5am) to get to the notch on the north ridge. The Irvis crampons using the Flexlock front (strap on) and Leverlock rear (clip on) bindings were quick to fit and rock solid, despite the two halves being held together with a piece of string! They felt completely secure, even climbing the rock section between the two snow slopes where I used the front points on small edges. It felt like a boot/crampon combo that I could use for longer, harder snowy routes without difficulty. The descent back down the mushy snow slopes in the afternoon were also reassuring, with the stiffness and good edge of the Vibram sole giving plenty of purchase and the neoprene cuff kept the snow out. Given all the ups and downs required to get back past the Sasc Fura hut to Bondo, carrying a reasonably heavy rucksack and having worn rock boots for 15 hours the previous day, my feet were in good shape when we got back to the car.