Don't take this as fact, this is my opinion based on my years of teaching and the teachers I had to work with.
I think push-in can really benefit the students, providing a certain number of factors are present. 1) There is high-quality, small group reading instruction geared to the students' reading abilities. 2) Teacher is not territorial about the classroom, and is welcoming to the Title I teacher. 3) Teacher is not leaving the room when the Title I teacher appears. 4) Title I teacher is responsible for the identified Title I students and their learning in a supplemental situation.
I have had to work around those obstacles. I do small group instruction, pull-out. For some of my students, it's the only high-quality reading instruction they get in a day, despite regulations to the contrary. That's reality. The best thing to do is what's best for the students. You would have to try to assess what you are going into and decide.
In order to counter the "stigma" of being pulled out, I work hard to make my reading groups fun, to the point that I have other students begging to be let into my reading groups. I'm not bribing the kids with candy or gum, and we rarely play games. When we do, they are games that deal with making or reading words. I give the kids what they don't know they crave, and that's individual attention. Every bit of reading instruction is geared to the student's level and needs. I listen to so many stories that you might wonder how I find time to teach. I thank every child that chooses to hug me, and I get many. I tell them often how much I love to read, and that I read everything.
I make a point of giving my director a list every December showing how much growth my students have shown in the 3 months they have have reading groups with me. The evidence always support my program, because it is what works with the teachers I have to work with, the kids I see, and how I teach.
Good luck! Let us know how you'll be doing your reading.