ILR - SET(M) vs SET(LR)

hi,
I am completing my 10 year stay in UK (Sept'2011 - 2021) in the next two weeks. I have been on various dependent visas including PSW Dependent, Tier 2 dependent, FLR(M). FLR(M) is the current visa I am on.

I am also completing 5 years on my FLR(M) in Oct'2021. My spouse is a British citizen now.

Question is - Can I apply for ILR on the 10 year stay route in Sept'21 or do I have to use the SET(M)?
When I read the rules it says any legal stay (with some caveats such as not being out for more than ~18 months out of UK) will make one eligible for ILR. However I also got the feeling that taking the FLR(M) resets your immigration clock or that if you are on FLR(M), you should only use the SET(M) route to apply.

Any guidance will be extremely helpful.

Summary -
Current visa- FLR(M) since Oct 2016
Stay in the UK - since Sept 2021 (on various dependent visas)
Questions -
1) Which ILR route should I use - SET(M) or ILR (10 year stay)
2) If both are possible - any pros and cons between the two routes (time taken for decision, application length, cost of application etc.)

Question is - Can I apply for ILR on the 10 year stay route in Sept'21 or do I have to use the SET(M)?

Your choice which one you choose. If you meet the requirements of either, you can apply via either route.

When I read the rules it says any legal stay (with some caveats such as not being out for more than ~18 months out of UK) will make one eligible for ILR.

The absence limits for ILR based on long residence is NOT 18 months (not sure where you got this from). You cannot have more than 540 days absence in the WHOLE 10 years and no single absence of 180 days or more at any time in the 10 year period.

However I also got the feeling that taking the FLR(M) resets your immigration clock or that if you are on FLR(M), you should only use the SET(M) route to apply.

It resets the 5 year ILR route when you switch to FLR(M) and NOT the long residence route.

1) Which ILR route should I use - SET(M) or ILR (10 year stay)

Your choice. ILR long residence has less paperwork to submit.

2) If both are possible - any pros and cons between the two routes (time taken for decision, application length, cost of application etc.)

All ILR applications cost the same and can take up to 6 months. It depends on what service you choose and pay for. Both routes lead to the same end results. There is no 'hidden catch' if that is what you are thinking.

Thank you - that is really helpful.
I will initiate the SET(LR) application process.

(also on the 18 month reference I made - I should have been clearer - absence of 540 days cumulative over 10 years - just laziness on my part to type the rules - apologies)

Firstly thanks to all the people who have provided tips on getting priority service appointment. I need my travel documents for business travel so couldn't afford to be waiting for 6 months from application for a decision.

Logged in at 1AM BST exactly as many people suggested on the forum and went to the 'Pay' section of my application and got the priority service option.

Now that I have submitted my application something is bugging me and I thought I need to get this cleared by the experts.

If my date of entry in the UK was 06 Sept 2011, I am assuming I am eligible to submit my application 28 days prior to the completion of my 10 years stay in UK - i.e. any day from 09 Sept 2021? Is my understanding correct?

Hoping this will allow to settle my nervousness on a rejected application.

You can apply early and as long as your day of the decision is within 28 days, you will be fine