After a brief trial of this combo from HEAD these are my initial thoughts:
Freedom of movement in the arms. I place high value on this, you can't get any freer other than having no top on at all. If you can cope with the temperature of water then it's worth considering. Most swimruns in Northern Europe have a water temperature between 10 and 18 degrees celsius. When making your judgement call on thickness/type of wetsuit don't just consider the headline water temperature, consider time in the water for any single leg. For example I swam Uto (10 degrees) in 1 mm neoprene but because the swim distances were pretty short I never felt that cold. Whereas on the final swim on Scilly (water temperature around 14 degrees, same 1mm neoprene) I got pretty cold, it was over 2.5km and we were slowing up. Also consider the length of run before the next swim. Race organisers often put a long run in between any long swims so that you get a chance to warm back up, but it's not a given.
The half-zip on the front is definitely better than a back zip, but not as good as a full zip on the front. As there are no arms it does make it easy to peel down to the waist. I wouldn't let the half zip put you off. I need to experiment more with this on longer runs...
After jumping/diving in I found that some water can "ride up" the waist. Possibly using a race belt would help to keep a seal around the bottom of the top (which you will use if you are towing anyway - highly recommended!)
The pants come in 3/4 length allowing the individual to cut where decided. Most swimrunners will cut just above the knee, particularly if partaking in longer runs. The extra neoprene on the front of the thighs definitely gave extra buoyancy and felt good to run in too. Again I will need to experiment with some longer runs.
The neoprene was soft and flexible and definitely felt fast in the water.
In summary If you were only going to have one swimrun wetsuit I wouldn't recommend this one. However if you were going to have two this would be a great 2nd as it is very versatile. I expect there's some swimruns in Southern Europe where you might just want to race in the pants. I'd even consider using this wetsuit combo at Uto as the swims are so short, but that wouldn't be for everyone.
I will race in this at some point this year and only then will I have a full and valid review for you...
UPDATE! I raced in this combo at OtillO Hvar 2017. Top: It felt quite cold after the long swim (approx 3km) - I think it's a combination of the no arms and the fact that water can seap in at the waist/lower back. Bottom: great for swimming, less so for running. I'm unlikely to use this combo again, I'll keep it for training but the HEAD Aero is much better for racing.