Did I miss the part of this story where they said they had nonstandard vesting? The industry standard is 4 year vesting, month by month, with a 1-year cliff. The traditional horror story is employees being fired just before they cliff.
Whether this particular stock will go up or down after the IPO is any-body's guess.
What does it cost to transfer stock in the US in a privately held company? Here in Europe it can be up to ~$1K to transfer stock in a GMBH or BV, other countries more or less depending on the local situation regarding notary public roles and rates. In a public company it is dirt cheap but this is prior to IPO.
That + accelerated vesting in case of wrongful termination or termination without cause can be reason enough to batch share vesting events.