TINYINT vs Nullable BIT performance in MS SQL Server
It's highly unlikely that there is a material performance difference here.

So the choice is between 

create table AppUser
(
  Id int identity primary key,
  Name nvarchar(200) not null,
  UserAccepted bit null
)


And

create table UserStatus
(
  Id tinyint primary key,
  Description varchar(200)
)

create table AppUser
(
  Id int identity primary key,
  Name nvarchar(200) not null,
  UserStatus tinyint not null references UserStatus default 0
)


And while one might be preferable in your particular application, they are both reasonable designs.