I'm am really struggling to get my head around the MFP fitbit calorie scenario.
After reading through many past posts I have set my fitbit calorie goal to my TDEE with a 250 calorie deficit.
It looks as if I was under eating - so maybe that's why I've been plateauing for almost 3 months. I've set MFP goal to the TDEE less 250 ( 1673)

Yesterday to add a bit of variety I did some strength / cardio using Kineses , I logged it as strength training and fitbit based on my times said I burnt 109 calories ( my calories burnt for the day were 2145 ) I'd done the same the day before logged kettlebells as strength training and based on times , it said I burnt 163 calories ( calorie burnt for the day 1832)

I'd read that some people set the timer and log an activity , so for my 1 hour spinning session , I used the timer and it logged 8485 steps and a 466 calorie burn for that 1 hour session - but my calorie burn for the day so far is only 1481 so far , which seems odd as I've worked my little butt off today .

So .... should I log exercise as an activity with the timer or log the times ?
are my steps waayyy out today because spinning has been counted as steps and activity?
should my calories burnt be the same as my TDEE and my consumption be my "goal" ( TDEE less 250) or have I got it all very very wrong?!?!?! If I'm supposed to eat back a cardio burn , how do I do that if my daily burn in currently only 1481

I'm really sorry if the questions have been asked 100 times over , I've been looking through posts in all sorts of discussions and my brain is frazzled .
thank you for any help at all !

I use to use the timer a lot to see whether I needed to log an activity. The timer just gives you a record of your fitbit stats in that time period--it doesn't change anything. If it is an activity that fitbit cannot track well, you might want to log it for a more accurate TDEE. Of the activities you mentioned:

Strength training: Fitbit won't track this well as it is a non-step, resistance based activity. You may get step credit for some exercises (i.e. step ups or walking lunges", but other exercises it may not pick up any activity at all. You might want to log strength training. I say might because some people don't count calories from strength training and do fine. I personally log it, how important it is depends on the type of strength training you are doing, your goals, how big a deficit you are aiming for, how much strength training you do. I don't know what Kiness is. Fitbit does well with activities that can be translated into steps like walking, running, skipping, hopping, marching, jogging, jumping (i.e. jumping rope, I think it may underestimate some plyos). and where there is no added resistance--just your body vs. gravity (and steplike movements are involved).

Kettlebells: you would want to log though if you are doing fast swings it may credit steps for swings. When I was doing 100 swings as a challenge it would credit steps in that time--but it would under credit the effort/calorie burn. I would log kettlebells as circuit training if it is a fairly no-stop workout where you alternate between lower and upper body exercises rather than taking rests. That type of kettlebell workout puts and keeps my heart rate similar to running, but I think "circuit training" is the most appropriate database entry. You should see very active minutes for the workout. If it is more like a slower paced, traditional strength workout just using kettlebells instead of dumbells with rests after each set, you probably logged it right.

Spinning you also want to log. It is aerobic exercise, but it doesn't involve step like movements. I've worn my fitbit One to spin class and was credited 2000 steps for a vigorous 1 hour class. This was like fitbit credited me for walking for one hour at a speed of 1mph. The calorie burn was 150 calories lower than my heart rate monitor's estimate for that workout. That is actually the biggest difference I've seen (even bigger than strength training--though a HRM isn't accurate for strength training). I would probably logit by the distance covered in the class, but I think the database has an entry for spin class.

So it seems that most of your intentional exercie are activities you need to log as fitbit wouldn't track them well. So likely the difference in fitbit calorie burn may have been that it did better with some activities than others. The fitbit burn is largely based on how much and how fast you move each minute (if it is a movement the ftibit can sense where you wear it). The other possibility is that your activity outside of your intentional exercise varied in those days. I think if you logged, your fitbit burns will be higher.

But if you are using a TDEE method, do not log exercise to MFP. MFP will add it on top of your allowance. With a TDEE method it is intended that you choose an activity level inclusive of your exercise and general activity. So if you log, log to fitbit. Now the problem is you will see an adjustment if your fitbit burn is higher than MFP expects. What MFP expects is not your custom allowance, it is the "calories burned from daily activity" in your MFP goals page. It is based on the most recent activity level you were set on MFP (I think sedentary if you never chose a different level). So you won't want to eat any adjustment calories if you chose the correct TDEE. I would still log non-step exercise to fitbit and use your average fitbit burn for the week as your TDEE (it is listed in the weekly reports fibit emails you). Whatever you do, do not do the thing where you log your exercise to MFP as 1 calorie. That may be fine for TDEE followers without fitbit devices, but if you do that you will reduce your exercise calories to 1 calorie (which is no doubt even lower than your BMR) and will end up with a very low fitbit TDEE as a result.