ACT stance towards the practice of metta?
OK, so we know ACT isn't Buddhism. Even so I'm curious as to whether RFT and ACT imply any particular stance towards the practice of metta, or loving-kindness.
In the Therevadan and Tibetan strains of Buddhism, this can range from the recital of phrases wishing health and well-being towards others, to prolonged imaginal exercises in which we examine our attitudes towards others, with the goal of undermining our natural tendency to favor friends over strangers and enemies.
Various assumptions are invoked during the latter process to favor a more inclusive and generous attitude, e.g. that countless reincarnations have occurred in which everyone on the planet has been cast in different relationships with each other, making the current arrangement both arbitrary and temporary. Western devotees tend to doubt the idea of actual reincarnation, but indulge it while practicing metta to improve effectiveness.
There may be no clear or "official" answer here - but I'd be curious as to what the many Buddhist-friendly practitioners in the ACT community think. Is metta the manipulation of context, or of thoughts? Also, assuming metta is generally helpful and healthy, is this particular practice an advantage that Buddhism has over ACT?

Metta and relational frames.
Is metta the manipulation of context, or of thoughts?
Practising Metta may impact on the relational frame form...ie impacting on changing the conceptualisation of potential emotional relationship. Practicing metta may restructure the emotional content within the relational frame.
To my way of thinking relational frame theory requires a series of contextual/emotional maps that operate within the relational frame. Metta reconceptualises the content of the relationship inmpacting on thoughts and reformulating the context.
Also, assuming metta is generally helpful and healthy, is this particular practice an advantage that Buddhism has over ACT?
ACT would look to address values and implementing commitment or purpose to the vlues. If Metta is not a part of an individuals value then it cannot be practiced within ACT. If you are a Buddhist the practice of loving kindness is essential. Maybe it is the same as "love your neighbour" or "love your enemy" within Christianity (alongside forgiveness). It reformulates the content of the relation frame and may create a new map (if practioners believe in these.)
Good thing someone asked this...
I was about to ask the same question. Pardon me that I don't quite understand RFT yet, but did you mean to say that practicing Metta as a manipulation of context is better than doing so as thought manipulation?
I have only finished reading "The Happiness Trap" by Russ Harris (Mr. Hayes' book is still on the way, won't be here until early next month) and so my understanding is just enough to ask this following question: Will practicing Metta, wishing one's self to become better, lead into the "happiness trap" because it tends to be a control strategy?
Please advise.
Thanks!
metta is as metta does
In the Christian tradition, we hear things like "love thy neighbor as thyself" and in Buddhism, that love/joy/nondiscernment is ever-present if we can wake up to it through such practices as metta. From an ACT stance, metta is as metta does. How does the context feel when you practice metta? :)
"Metta" as valued action
If someone values "metta" (loving kindness), making a commitment to putting it into action might be ACT consistent.
Likewise, if someone values being a devoted employee, making a commitment to putting that into action might be ACT consistent.
Different religious teachings often appear to embody similar values, but I don't think the ACT model need adopt Buddhist, Hindu or any other religious notions.