An apparatus for use with a device for delivery of a therapeutic fluid into a body of a patient and/or for sensing of a bodily analyte, the apparatus comprising: (i) a disposable cannula cartridge unit comprising: (a) a penetrating cartridge comprising: a subcutaneously insertable element; and a penetrating member for penetrating the skin of the patient; and (b) a protective member having an elongate body including a lower open end and at least one window to allow access to the penetrating cartridge for protracting the penetrating cartridge toward the body of the patient, the at least one window being selected from the group consisting of: an upper open end and a longitudinal slit disposed in the protective member, the elongate body housing the penetrating cartridge such that the subcutaneously insertable element and the penetrating member are protractable from the elongate body through the lower open end to penetrate the skin of the patient, with the penetrating member being subsequently retractable whilst the subcutaneously insertable element is retainable in the body of the patient; (ii) an insertion device including a displacement mechanism adapted to allow access to the penetrating cartridge through the at least one window, the displacement mechanism having a loadable spring for forcible displacement of the penetrating cartridge toward the body of the patient, the insertion device being configured to allow: automatic advancement of the subcutaneously insertable element and the penetrating member from the protective member and into the body of the patient, when the disposable cannula cartridge unit is loaded into the insertion device; and subsequently retract the penetrating member back into the protective member, whilst the subcutaneously insertable element remains in the body of the patient. (i) a disposable cannula cartridge unit comprising: (a) a penetrating cartridge comprising: a subcutaneously insertable element; and a penetrating member for penetrating the skin of the patient; and (b) a protective member having an elongate body including a lower open end and at least one window to allow access to the penetrating cartridge for protracting the penetrating cartridge toward the body of the patient, the at least one window being selected from the group consisting of: an upper open end and a longitudinal slit disposed in the protective member, the elongate body housing the penetrating cartridge such that the subcutaneously insertable element and the penetrating member are protractable from the elongate body through the lower open end to penetrate the skin of the patient, with the penetrating member being subsequently retractable whilst the subcutaneously insertable element is retainable in the body of the patient; (a) a penetrating cartridge comprising: a subcutaneously insertable element; and a penetrating member for penetrating the skin of the patient; and (b) a protective member having an elongate body including a lower open end and at least one window to allow access to the penetrating cartridge for protracting the penetrating cartridge toward the body of the patient, the at least one window being selected from the group consisting of: an upper open end and a longitudinal slit disposed in the protective member, the elongate body housing the penetrating cartridge such that the subcutaneously insertable element and the penetrating member are protractable from the elongate body through the lower open end to penetrate the skin of the patient, with the penetrating member being subsequently retractable whilst the subcutaneously insertable element is retainable in the body of the patient; (ii) an insertion device including a displacement mechanism adapted to allow access to the penetrating cartridge through the at least one window, the displacement mechanism having a loadable spring for forcible displacement of the penetrating cartridge toward the body of the patient, the insertion device being configured to allow: automatic advancement of the subcutaneously insertable element and the penetrating member from the protective member and into the body of the patient, when the disposable cannula cartridge unit is loaded into the insertion device; and subsequently retract the penetrating member back into the protective member, whilst the subcutaneously insertable element remains in the body of the patient.