Difference between Speedmaster Pro 3572.50 and 38705031?

Hi everyone!

I have a quick question for the Speedmaster experts on the forum.

I am contemplating buying a Speedmaster Pro for my 30th birthday, in a few months.

I saw several second-hand Speedmasters Pro at my local vintage dealer:

- several models 3572.50 (year not indicated)

- a 2009 model 38705031 at 4 200 euros taxes included (i.e. 4 962 US dollars, tax. included) , cheaper than the 3572.50 models.

Could you please tell me the differences between these two models?

It seems to me that both of them have a 1861 movement... Is this correct?

What are the differences in terms of technology, reliability, price of parts, etc.?

Thanks in advance for your help!

I think the 3572.50 is a Hesalite 1863 model = sapphire case back and slightly nicer finish 1863 rather than 1861. on steel bracelet.

The other is maybe a Hesalite 1861 with leather strap.

I think the biggest difference is the 3572.50 has display caseback, whereas the 3870.50 does not.

I researched 3572.50 before buying one for myself. AFAIK, there are (at least) these three versions:
a) Hesalite, gold 863 movement, tritium dial/hands (95-97)
b) Hesalite, rhodium 1863 movement, tritium dial/hands (96-97)
c) Hesalite, rhodium 1863 movement, Superluminova dial/hands (97-03)

This may not be perfectly accurate, but should be close. I chose to get a) and I love it.

Thank you all for your answers. This forum is truly helping for beginners!