I recommend using flaps during instrument training.
It gives the student plenty of time to open up the textbooks and study for the written while on final approach.
Ha ha, yes there is a 12NM arc transition to an ILS/LOC approach in our area, it is 16NM from IAP to FAF, takes a long time, +10 mins to be exact. Enough to set up for approach and missed, and have a snack. 90 kts (no wheel pants) is also cruise speed. It makes it simple. Since 85kts is Vfe I don't like pushing limits just to reduce wear and tear. 90 kts is the sweet spot I already sorted out before I posted my question. I was curious. Final approach segment is same for a C172 or even C182, 90 kts. However C182 has KIAS flap extension of 140kts (10) and 95kts (40). So yes I use flaps 10 or 20 so I can keep power up. The C182 I fly has a STOL kit, droop LE, stall fence, seals) so the stall speed is ridiculously low. It basically will not fully stall unless you really get agro.
I discuss the down side of clean approach in C152... Slowing down to land.
C152 you get to mins and see runway, but just barely, depending on approach you are (for an example) on 3 deg path, 1.5 nm from TCH, 300-400 feet above THC, at 90kts clean. If this was a VFR student I would have coughed and said something long before. However this is IAP and not short feild STOL landing competition.
Slowing to flap extension is the issue or trick. You can't "go down and slow down", at easily, even in a mighty C152. To lose 5kts clean in a constant descent even at idle is not instantaneous if ever depending on ROD. It is going to take some reduced ROD or level off (or slip) to bleed off speed.
1)
Obviously pull power back (w/ Carb Heat) smoothly and slowly. Note: 90kts at 450fpm descent, RPM is top of green, but recommend CH for whole approach. Note not a big fan of to the stop idle on approach, like to leave an elevated RPM.
2)
Option 1 - Momentarily at Mins, Rwy insight, reduce ROD or level off, slow below 85kts, bring in flaps in, continue descent to runway.**
Option 2 - Start round out / flare slightly higher than normal, bring flaps in below 85kts. Extend flaps in steps, not all at once, guard against asymmetric issue.
Option 3 - Land clean at slightly higher speed
** They are all viable, but reducing your descent or leveling off just below MINS (assume we are IMC with minimum visibility), you may go back into cloud (ragged ceiling base) or lose sight of runway (slant range visibility). Also not a stabilized approach. If it is VFR sure do that, and accept a slightly steeper or higher path to touchdown.
Flare in ground effect clean, you going to use more runway. This may be OK w/ long runway and target FBO at far end of Runway. However embarrassing to go off far end of 8000 ft runway in a C152. Adding flaps changes pitch trim. So clean may not be a bad option, touching down may be 6kts faster.
IMHO best "Plan A" is in-between Option 1 & 2. Say 100 feet above THC, than start reducing rate of descent or almost level, slowdown, configure flaps, establish normal landing speed, 60-65kts 30deg, and then add partial power as needed for a "normal" landing, albeit further down the runway than you might VFR. A Fwd Slip is an option but that is a different topic. Should not be necessary, but IFR does not mean not using basic VFR pilot skills. Anyway 2000-3000 feet of Rwy is enough to land a C152 from 90kts clean on an IAP. I have landed C402 and Cessna Citation on 3000 ft. BUT like the large airliner I fly you are fully configured and at landing speed by 1000 feet HAT. So you can land a C152 on 3000 ft (the min runway length for an IAP runway, most are 4000-5000 ft or longer).