BLUF: Choice between current position in larger business, limited opportunity vs. key role in small business, same salary + potential part ownership.
Hi all, I have a very particular decision to make in the next couple of weeks and would appreciate any thoughts or experiences.
I'm in a management position with a 60-person business and have established a particular niche. A merger at the start of the year has changed the nature of the business and while I don't believe my role to be at risk, it is likely to remain a niche, one that will need to adapt to the needs of the new business and will likely be redefined in the coming months.
I have been approached by a former boss to join and help grow his fledgling business, with the promise of profit sharing and potentially part ownership (details to be nailed down). The salary offer is to match my existing package, i.e. no change to base.
So my choice is between a relatively secure - but niche - role in a larger business, or a central role in a growing business (I'm conscious of the rule has been touted somewhere in MT/CT about not moving for less than 25% than current salary).
Not expecting anyone to make the decision for me :) - but welcome any relevant insights.
Thanks in advance.

Relationship?
Never done it, never contemplated it. However, one question I would ask is why don't I work for this person anymore? Did he get promoted or did you leave? If he left, were you secretly thrilled/relieved? Or, is this someone you would have followed to the ends of the earth? I have a boss like that. Follow her anywhere she asked.
What was your relationship before, because it'll be "that" again.
I would also ask myself if I am cut out to be an entrepreneur?
Hope that is helpful.
Relationship = good
Thanks for the reply.
He left the business of his own accord, and my relationship with him was always good albeit he would view me as a subordinate. This plants a seed of doubt as to the relationship ongoing. Also, I've established a good reputation for what I do, but not entirely sure he is aware of everything I've achieved. My fear is he might simply need to fill a short term need.
All that said, I would trust him completely.
Risk vs. Reward.
A smaller company is generally going to be riskier in the short term, but may also provide you with the opporunity to develop a wider skill set. This will actually reduce your long term career risk. If you are in a niche in the existing business, is it also a pigeon hole? Might it disappear or limit you future career opportunities? I myself have a tendency to prefer a broader persepctive position, but I also think that gives you a better ability to pivot if things change at your company or in your industry. An opportunity for ownership has its own risks as well, but also a potential for significant gain if things go very well.
Good summary!
That about sums it up. The niche will almost certainly become a pigeonhole, or morph into something that I have no interest in - if it were an opportunity I would pounce on it, but the whole thrust of the business has changed overnight with the merger.
The offer is to take the lead in the smaller business, doing what I already do, which will be central to operations. On further reflection in the last couple of days, that's definitely where the opportunity lies.
Read a great quote during the week, something along the lines of "When approaching difficult decisions, go where the fear is".