diff --git a/lib/iris/common/mixin.py b/lib/iris/common/mixin.py
index bcdc7f5f01..ce8e7a520c 100644
--- a/lib/iris/common/mixin.py
+++ b/lib/iris/common/mixin.py
@@ -179,6 +179,7 @@ class CfUnit(cf_units.Unit):
         @classmethod
         def from_unit(cls, unit: cf_units.Unit):
             """Cast a :class:`cf_units.Unit` to an :class:`Unit`."""
+            unit = cf_units.as_unit(unit)
             if isinstance(unit, CfUnit):
                 result = unit
             elif isinstance(unit, cf_units.Unit):
@@ -234,6 +235,12 @@ def _round(date):
 
             return result
 
+        def __repr__(self):
+            # Adjust repr to look like the parent class, to avoid many CML errors.
+            string = super().__repr__()
+            string = string.replace(self.__class__.__name__ + "(", "Unit(", 1)
+            return string
+
 
 if cfpint is not None:
 
@@ -521,7 +528,7 @@ def is_vertical(self):
 
 
 # FOR NOW: insist on pint units
-_DEFAULT_UNITCLASS: type = CfpintUnit
+_DEFAULT_UNITCLASS: type = CfUnit
 
 # And force pint too.
 # TODO: since we may have seen problems with doing this dynamically, this could affect
@@ -629,8 +636,8 @@ def units(self) -> cf_units.Unit | cfpint.Unit:
 
     @units.setter
     def units(self, unit: cf_units.Unit | cfpint.Unit | str | None) -> None:
-        # unit = cf_units.as_unit(unit)
-        self._metadata_manager.units = default_units_class().from_unit(unit)
+        unit = default_units_class().from_unit(unit)
+        self._metadata_manager.units = unit
 
     @property
     def attributes(self) -> LimitedAttributeDict:
diff --git a/lib/iris/tests/unit/common/mixin/test_pintunits.py b/lib/iris/tests/unit/common/mixin/test_pintunits.py
index 359c4c175e..c7cdaaed3a 100644
--- a/lib/iris/tests/unit/common/mixin/test_pintunits.py
+++ b/lib/iris/tests/unit/common/mixin/test_pintunits.py
@@ -1,3 +1,12 @@
+# Copyright Iris contributors
+#
+# This file is part of Iris and is released under the BSD license.
+# See LICENSE in the root of the repository for full licensing details.
+"""Stopgap testing for pint units.
+
+So far, only a few specific things are tested.
+"""
+
 from datetime import datetime
 
 import cf_units
@@ -29,7 +38,9 @@ def test_nounit_eq():
 
 def test_calendar():
     unit = CfpintUnit("days since 1970-01-01", calendar="360_day")
-    assert repr(unit) == "<Unit('days since 1970-01-01', calendar='360_day')>"
+    # NOTE: no <>, due to "backwards compatibility" for assert_CDL
+    # TODO: remove the CfpintUnit._REPR_NO_LTGT
+    assert repr(unit) == "Unit('days since 1970-01-01', calendar='360_day')"
     # TODO: should really add the calendar to the string format
     #   I think this is a bit horrible,
     #   .. but it is cf_units behaviour + currently required for correct netcdf saving
diff --git a/lib/iris/tests/unit/test_Future.py b/lib/iris/tests/unit/test_Future.py
index e9ce4af222..445e8bf40d 100644
--- a/lib/iris/tests/unit/test_Future.py
+++ b/lib/iris/tests/unit/test_Future.py
@@ -122,7 +122,8 @@ class Test__str_repr:
     def _check_content(self, future, text):
         assert text == (
             "Future(datum_support=False, pandas_ndim=False, save_split_attrs=False, "
-            "date_microseconds=False, derived_bounds=False, lam_pole_offset=False)"
+            "date_microseconds=False, derived_bounds=False, lam_pole_offset=False, "
+            "use_cfpint_units=False)"
         )
         # Also just check that all the property elements are included
         for propname in future.__dict__.keys():
diff --git a/noxfile.py b/noxfile.py
index 4d733fa2d4..705446cb1e 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -6,6 +6,7 @@
 
 import hashlib
 import os
+import pathlib
 from pathlib import Path
 
 import nox
@@ -181,6 +182,31 @@ def tests(session: nox.sessions.Session):
     prepare_venv(session)
     session.install("--no-deps", "--editable", ".")
     session.env.update(ENV)
+
+    # HACK EXTRAS: install pint; download cfpint + make it importable with a pth
+    session.conda_install("pint")
+
+    def expth(pth):
+        return str(pathlib.Path(pth).expanduser().absolute())
+
+    session.run("mkdir", "-p", expth("~/extra_installs"), external=True)
+    session.run(
+        "git",
+        "clone",
+        "https://github.com/SciTools/cfpint.git",
+        expth("~/extra_installs/cfpint"),
+        external=True,
+    )
+    session.run(
+        "mkdir",
+        "-p",
+        expth(f"~/.local/lib/python{session.python}/site-packages"),
+        external=True,
+    )
+    path = expth(f"~/.local/lib/python{session.python}/site-packages/cfpint.pth")
+    with open(path, "w") as f_out:
+        f_out.write(expth("~/extra_installs/cfpint/src"))
+
     run_args = [
         "pytest",
         "-n",