Setting up a SEPP would be your last choice if you can comfortably avoid it because these plans are rigid and if you don't meet all the requirements, you will be hit with retroactive penalties and interest on those penalties. But if you happen to have all your assets tied up in retirement plan, a SEPP can be the only way out. If you qualify for the separation from service at 55 exception, the next step is to confirm that you can take flexible distributions from that plan as you need them and avoid a SEPP. However, if the plan provisions require a lump sum distribution or other inflexible withdrawal option, then you would not establish a SEPP plan from the 401k, you would roll it over to an IRA and establish the plan from your IRA account. You have much better control of an IRA account than a 401k plan, which can change providers in the middle of your plan. For examples of IRA flexibility, if your distribution was too large for some reason, with an IRA you could roll the excess back within 60 days, but would not be able to from a 401k plan.
Due to the record low interest rates, a SEPP plan will only generate little more than 4% of the account balance in annual distributions. This may not be enough, and if so it increases the chance you will bust the plan. Conversely, if your account balance will generate more than you need, you should partition your IRA into one for the SEPP with the appropriate account balance and another for emergency needs that you get penalized funds from but such access would save your SEPP plan from failure due to taking out an emergency distribution.