We (Pedro Mira’s group from Spain) have been in Sprengisandur Tour with Arnar.
We are very happy with the experience (in spite of windy weather), in particular with Arnar, a great guide and a very nice person. 
We haven’t had any significant problem, all ran OK. Thank you specially for the gluten free diet; it has been crucial to enjoy the trek for me.
Just a minor suggestion: something like Tang or any product with salts or similar to put into snow boiled water would be recommended and healthier.
We are now thinking in Vatnajökull for the future…
Thank very much.

Best regards 

Alicia Valencia and Carlos Villalain
Spain

Sprengisandur - Traverse of the Icelandic Highlands Tour