The phrase "are usually complex to" is correct and usable in written English.
It can be used when describing something that typically involves a high level of complexity or difficulty in understanding or executing.
Example: "The processes involved in software development are usually complex to manage without proper tools."
Alternatives: "tend to be complicated to" or "are often difficult to".
Haem is rarely found free in serum and it is usually complexed to one of several haem-binding proteins, including Hb and haemopexin.
HTA and policy decisions are usually complex due to the multiple aspects considered and the extensive amount of evidence.
However, these reaction processes are usually complex or difficult to control.
However, these methods are usually complex and difficult to perform.
In metazoans, the biological and biomechanical processes that underlie such three-dimensional (3D) developmental events are usually complex and difficult to investigate.
The bending and folding of a sheet of cells is fundamentally a biomechanical, supercellular process involving coordinated changes in the shapes of many neighboring cells that interact; however, the biological and biomechanical processes that underlie such three-dimensional (3D) morphogenetic events in metazoans are usually complex and difficult to investigate [ 2- 7, 9- 19].
However, software applications for detailed spino-pelvic analysis are usually complex and not applicable to routine clinical use.
Key enzymes are usually complex proteins that, in addition to the site at which the catalytic process occurs (i.e., the active site), contain sites to which the regulatory metabolites bind.
The Say-on-Pay and golden-parachute provisions are inherently limited, she believes, both because the votes are nonbinding and because such votes require shareholders to make yes-or-no responses to what are usually complex questions.
Their configurations and joints are usually complex and require a high level of craftsmanship to assemble.
