Papagigo,
Merlin Series are work horses! Many older Merlin systems & Phones from the 80's & 90's are still in use!
The only issues I've seen with Merlin Magix have been the ETR016 cards, and occasionally a hard drive failure in voicemail.
Magix 44xxPhones are very reliable, and usually prefered, even with IP office! IP46xx/56xx Phone are very expensive!
4412D & 4424D Phones are mostly in My Home Office.
Only Issue with Legend is the MLX10D Phones, I have seen quite a few of these go bad with dead keys, leaving You only able to answer calls. The MLX10DP were much more reliable.
Andre